Phenolic Tanning and Pigmentation of the Cuticle in Carcinus maenas

333 

Phenolic Tanning and Pigmentation of the Cuticle in 

Carcinus maenas 

By G. KRISHNAN 

{From the Dept. of Zoology, University of Manchester; present address, Dept. of Zoology, 

Presidency College, Madras) 

SUMMARY 

I . The histochemistry of the cuticle in different stages of the moult cycle of Carcinus 

maenas is described. 

3. The newly formed cuticle of a crab exposed at moulting shows evidence of 

phenolic tanning in the epicuticle. 

3. The subsequent tanning of the pigment layer of the endocuticle is confined to a 

brief period immediately after moulting. 

4. The polyphenol oxidase of the epicuticle involved in tanning disappears soon 

after moulting, but some time later an oxidase is again indicated, this time in the 

pigment layer. It appears to be secreted by the tegumental glands. 

5. From the concurrent appearance of a polyphenol oxidase and tyrosine and the 

subsequent formation of dihydroxyphenols and melanin-like substances in the cuticle, 

it is suggested that the oxidation products of tyrosine are responsible for the pigmentation 

of the cuticle. 

6. Pigmentation of the cuticle is discussed in relation to phenolic tanning in Crustacea 

and Insecta. 

R 

INTRODUCTION 

ECENT work has emphasized the fundamental similarity of the crusta- 

. cean cuticle to that of insects (Drach, 1939; Pryor, 1940; Dennell, 

1947 b). The last-mentioned author in addition to confirming the occurrence 

of phenolic tanning in Crustacea has suggested that its mechanism may be 

essentially similar to that in insects. Notwithstanding the homology of the 

cuticle in the two groups mentioned above it is seen that in Crustacea tanning 

of the cuticle is much abbreviated, the prime cause of hardening being 

calcification (Dennell, 1947 b). In insects it has been shown (Pryor, 1940; 

Fraenkel and Rudall, 1940, 1947; Dennell, 1946, 1947 a) that the hardening 

of the cuticle is due to the passage into it of a polyphenol, the oxidation 

product of which forms cross-linkages within the protein phase of the cuticle. 

The other concomitant changes are the reorientation of the chitin crystallites, 

a loss of solubility of proteins and a darkening effect. It has been pointed out 

(Pryor, 1940; Pryor et al., 1947) that hardening and darkening of the cuticle 

of insects are the result of tanning, and it therefore appeared of interest to 

discover the relation existing in Crustacea between tanning and the formation 

of melanin-like pigments in the cuticle. 

[Quarterly Journal of Microscopical Science, Vol. 92, part 3, pp. 333-42, September 1951.]

334 Krishnan—Phenolic Tanning of the Cuticle in Carcinus maenas 

METHODS 

The material used in this work was the merus of the walking legs of 

Carcinus maenas, obtained from Plymouth. Paraffin, frozen, and hand sections 

were prepared for study of the cuticle. Dehydration was carried out with 

dioxane to avoid the undue hardening that may result from treatment with 

higher grades of ethyl alcohol. The stains used were Mallory's triple stain 

and Masson's trichrome stain. The oxidases of the cuticle were studied 

using the nadi reagent (a mixture of dimethyl-para-phenylenediamine and 

a-naphthol (Lison, 1936) on frozen and hand sections. Melanin-like substances 

were detected by the solvent action of ethylene chlorhydrin. In 

addition, a number of other histochemical reagents were used for the detection 

of fats, phenols, and amino-acids, and are mentioned in appropriate places 

in the text. 

outer epicubicle 

inner epicuticle 

endocuticle 

epidermis 

FIG. 1. Section through the newly formed cuticle of Carcinus maenas in the process of shedding 

the old shell. 

PHENOLIC TANNING AND DARKENING 

Dennell (1947 b) described the cuticle of Crustacea in the light of recent 

work on that of insects and brought forward evidence of the occurrence of 

tanning in the epicuticle and the outer layers of the endocuticle. The 

quinones responsible for tanning have been shown to be formed by the 

oxidative activity of a polyphenol oxidase which is located in the epicuticle in 

the very early stages after moulting. From the disappearance of the oxidase 

soon after moulting it appears that the tanning of the cuticle is a brief process 

confined to a period immediately following the formation of the new cuticle. 

With a view to throwing more light on this aspect of the problem, the cuticle 

was studied from its appearance at the time of moulting. 

The newly formed cuticle of a crab at the time of shedding the old shell 

(fig. 1) consists of a thin epicuticle and a homogeneous endocuticle staining 

red and blue respectively with Mallory's triple stain. Overlying the red epicuticle 

is a very thin blue-staining membrane, the outer epicuticle, whose 

integrity as a discrete layer is borne out by its separation from the inner 

epicuticle due sometimes to mechanical factors and noticed in fixed prepara-

Krishnan—Phenolic Tanning of the Cuticle in Carcinus maenas 335 

tions of the cuticle. The inner epicuticle even before the old shell is cast 

shows evidence of tanning. At this stage in frozen and hand sections the 

untreated epicuticle shows an amber coloration but the endocuticle is colourless. 

That the amber coloration of the epicuticle is due to tanning is indicated 

by the bleaching of the amber-coloured zone by diaphanol, which has a 

selective action on tanned regions. The occurrence of tanning in the epicuticle 

is further confirmed by the results obtained with the Millon and argentaffin 

reactions, both of which are positive, indicating the presence of aromatic 

outer epicuticle 


pigmented zone 

calcified zope 

epidermis 

begumenfcal gland 

FIG. 2. Section of the cuticle of a soft crab about two days after moulting. 

substances. The endocuticle is unaffected by such treatment. Staining of 

sections with Sudan black B. indicates that both the inner and outer epicuticles 

contain lipoid substances. Ferric chloride gives a slight green coloration in 

the inner epicuticle and in the outer layers of the endocuticle, indicating the 

presence of a dihydroxyphenol. This is consistent with the observation 

(Dennell, 1947 a) that tanning spreads inwards as a result of a wave of 

quinone formation induced by the polyphenol oxidase activity in the epicuticle. 

The presence of polyphenols in the outer layers of the endocuticle as 

indicated by the ferric chloride test suggests impending tanning of this region. 

Sections of the cuticle of a soft crab some time after moulting (fig. 2) show 

that both the epicuticle and the outer layers of the endocuticle are tanned. 

That the tanning of the cuticle is completed by this stage in the moult cycle 

is suggested by the lack of a reaction with ferric chloride, indicating the 

absence of a dihydroxyphenol. In the absence of an oxidase and extension of 

the tanned zone at this stage, dihydroxyphenols involved in tanning may not 

now occur in the cuticle. Fig. 3 shows a section of the hardened cuticle of


Carcinus in the middle intermoult stage. It corresponds to that given by 

Dennell (1947 b) of the merus of the first walking leg of Astacus. A comparison 

of a section of the hardened cuticle with the exoskeleton of a soft 

crab shows that the epicuticle and the tanned zone of the endocuticle are 

similar and changes are observed only in the rest of the endocuticle, which is 

considerably extended and differentiated into a calcified zone and a narrow 

•droplet at opening of 

tegumental gland 

outer epicuticle 


pigmented zone 

'junction between 

pigment zone and 

calcfh'ed zone 

calcified zone 

duct of tegumental 

gland 

non-calcified zone 

epidermis 

1mm. 

. FIG. 3. Section of the hardened cuticle of Carcinus maenas in the middle of the intermoult 

stage. 

inner non-calcified layer. At the junction of the calcified and pigmented layer 

is a narrow zone which stains intensely blue after Mallory stain. The ducts of 

the tegumental glands passing through the cuticle to open on its surface form 

a prominent feature of the sections. The contents of the ducts stain red with 

Mallory and at the openings of the ducts red-staining globules are often seen, 

and may represent the secretion of the glands. Their appearance recalls that 

observed by Wiggles worth (1947) in regard to the dermal glands of Rhodnius. 

The nature of the changes undergone by the cuticle during the intermoult 

stage after the initial occurrence of tanning are shown in Table I, which gives 

the results of histochemical tests on the cuticle at an early stage, middle 

stage, and a late stage in the intermoult period. 

The positive Millon and argentaffin reaction in the epicuticle and pigment 

layer is consistent with the observation that these regions are hardened by 

phenolic tanning at a very early stage in the moult cycle. The negative reaction


TABLE I 

Argentaffin 

test 

Millon's 

reagent 

Momer's 

reagent 

Ferric 

chloride 

Fehling's 

solution 

Nadi (without 

KCN) 

Cuticle after 

moult 

Early stage 

Middle , 

Late 

Early , 

Middle , 

Late , 

Early , 

Middle , 

Late , 

Early , 

Middle , 

Late , 

Early 

Middle , 

Late , 

Early , 

Middle , 

Late , 

Outer 

epicuticle 

+ + 

4" 4" 

4-4- 

4-4- 

4-4- 

+ _ 

— 

— 

— 

— 

_ 

— 

— 

__ 

— 

— 

Inner 

epicuticle 

4-4-4- 

4" 4- 4- 

4-4-4- 

4-4- + 

-t- + 4- 

' _ 

— 

— 

——_ 

4- + 

-|- -|- 

_ 

— 

— 

Pigment 

layer 

+ 

—(— —|— —)— 

4-4-4- 

4- 4- 

• 4-4-4- 

+ 

_ 

4-4-4- 

— 

— 

-)- 

_ 

+ + + 

4-4- 

Calcified 

layer 

— 

— 

— 

- 

_ 

— 

— 

— 

4.4- 

— 

— __ 

— 

— 

Noncalcified 

layer 

— 

— 

— 

— 

_ 

— 

— 

— 

_ 

_ 

— 

— 

_ 

— 

— 

with ferric chloride in the earlier stages of the intermoult period points to the 

absence of free dihydroxyphenols at this stage, though they reappear later. 

The presence of dihydroxyphenols at a comparatively late stage in the moult 

cycle appeared inexplicable in view of the observation that tanning is confined 

only to a very early stage after moulting. An interesting result was obtained 

by treating hand sections of the cuticle with the nadi reagent which gave an 

intense blue colour in the pigment layer of the endocuticle. The presence of 

an oxidase appears to be indicated by the inhibition of this reaction by 

potassium cyanide and by heating. Treatment of hand sections of the cuticle 

with aromatic substances showed rapid coloration with catechol, protocatechuic 

acid, and hydroquinone. Dennell (1947 b) observed that in Astacus 

and other decapods the epicuticle soon after moulting shows the presence of a 

polyphenol oxidase but later the nadi reaction is obtained even in the presence 

of cyanide. This later reaction is apparently due, however, to the presence of 

o-quinones, which are capable of oxidizing the nadi reagent, and is distinct 

from the true oxidase reaction mentioned above. The absence of a positive 

reaction with nadi some time after tanning has taken place, as has been 

observed in Carcinus, may be taken to indicate not only the absence of an 

oxidase, but also that the quinones which reacted at an earlier stage to give a 

pseudo-phenoloxidase reaction have now lost their reactive properties, possibly 

due to polymerization or to changes consequent on their condensation 

with the proteins of the cuticle. Later still, however, phenol oxidase reappears, 

now in the pigment layer, and represents either a fresh secretion on the part 

of the structures elaborating it, or secretion by some other structure. From an 

analogy with the condition obtaining in insects where the polyphenol oxidase


of the cuticle has been shown to be derived from the epidermis (Dennell, 

1947 a) it might be expected that this layer in Carcinus would be the site of 

elaboration of the oxidase. Treatment with nadi reagent did not give a positive 

reaction in the epidermis at any stage of the moult cycle, but the tegumental 

glands which.during this stage are found in an active secretory state gave 

with nadi a blue coloration which was thermolabile and cyanide-sensitive. 

The ducts of the glands penetrating the cuticle also gave a positive reaction 

apparently indicating the transport of the oxidase to the cuticle. Hand sections 

treated with catechol rapidly gave a dark brown coloration in the tegumental 

glands and their ducts, so confirming the presence here of a polyphenol 

oxidase. 

Previous work on tegumental glands records a wide range of functions 

performed by them. Yonge (1932) has given a critical and comprehensive 

account of the work of earlier authors and has suggested that the tegumental 

glands are primarily concerned with the secretion and preservation of the 

epicuticle. The intimate association of the glands with the cuticle led Dennell 

(1947 b) to point out that 'it is difficult to avoid the view that in Crustacea 

the activity of the tegumental glands is closely connected with the structure 

of the cuticle'. He suspected that if they are not concerned directly with the 

secretion of the cuticle, they may yet be related to the subsequent hardening 

by the elaboration of the oxidase involved in tanning. It is seen from the 

foregoing observation in Carcinus maenas that the tegumental glands secrete 

a polyphenol oxidase some time after tanning and are concerned with an 

aspect of cuticular development which, it will be shown in this paper, is 

related to pigmentation. 

TYROSINE AND MELANIN FORMATION 

In the search for a possible substrate for the oxidase occurring late in the 

development of the cuticle, it was of interest to note the positive reaction 

given with Morner's reagent in the pigment layer of the cuticle at this time. 

That the substance giving the green coloration with Morner's reagent is 

indeed tyrosine is confirmed by the use of a-nitroso-jS-naphthol which gives 

a red coloration with tyrosine in the presence of nitric acid (Feigl, 1947). 

The occurrence of tyrosine is in itself not surprising as Trim (1941) had 

already recorded its presence in the cuticle of the lobster. The condition 

observed in Carcinus recalls that found in Sarcophaga falculata (Dennell, 

1947 a), in which tyrosine accumulates in the outer endocuticle preparatory to 

the tanning of this region to form the exocuticle of the puparium. But in 

Carcinus the presence of tyrosine in the pigment layer, which has already 

undergone tanning, may. not have the same significance as in Sarcophaga. 

In the absence of any further extension of the tanned zone of the cuticle 

during the stages when the oxidase and substrate are present, it would appear 

that at this time they are not involved in further tanning of the cuticle. The 

assumption that a later process of tanning, if it occurs, may result only in an 

intensification of tanning that has taken place, seems inconsistent with the

Krishnan—Phenolic Tanning of the Cuticle in Cardnus maenas 339 

positive reaction obtained with ferric chloride in the endocuticle, showing the 

presence of free dihydroxyphenols presumably formed as a result of the 

oxidation of tyrosine by the phenolase. Tyrosine, as indicated by a feeble 

reaction with Morner's reagent, gradually disappears, although free dihydroxyphenol 

persists for some time. 

Additional support for this view is afforded by examination of sections of 

hard and thickened cuticle after prolonged treatment with diaphanol. Such 

sections show in the pigment zone and the calcified layer a black coloration, 

revealed by the disappearance of colour due to tanning. When such sections 

are treated with ethylene chlorhydrin, which is a solvent for melanins, it is 

observed that the black substance of the cuticle is rapidly dissolved. That 

melanin-like substances may be formed from dihydroxyphenols present in the 

cuticle is suggested by the observation that hand sections of the cuticle when 

treated with dihydroxyphenylalanine (DOPA) show within a few minutes a 

black coloration in the endocuticle. When such sections are treated with 

ethylene chlorhydrin, they are decolorized in a manner similar to that occurring 

in naturally blackened cuticles under such conditions. From the concurrent 

appearance of a phenol oxidase and tyrosine in the pigment layer and 

the subsequent formation of dihydroxyphenols and pigmented products, it 

may be justifiable to assume that tyrosine is oxidized in the cuticle to form 

dihydroxyphenols, giving rise to pigmented products of the nature of melanins. 

DISCUSSION 

Wigglesworth (1948 a) as a result of his observations on Tenebrio suggested 

that the tyrosine of the cuticle may give rise to melanins, for the regions of 

the cuticle which later become darkened show the presence of tyrosine. In 

Cardnus tyrosine is not found in the cuticle in the early stages of the moult 

cycle. A similar condition to that in Cardnus has been observed in Sarcophaga 

where no free tyrosine is found in the larval cuticle until just before puparium 

formation (Dennell, 1946). It may be inferred that the tyrosine of the cuticle 

is derived from the blood. Pinhey (1930) found that the blood of Maia 

squinado and Cancer pagurus contains about 0-004 P er cent, of tyrosine, at all 

stages of the intermoult period. Tyrosine estimation of the blood of Cardnus 

shows that it is similarly more or less constant at about 0-003 P er cent. If, as 

has been shown by Dennell (1947 a) and Fraenkel and Rudall (1947), the 

blood tyrosine is the source of the phenol involved in tanning of the cuticle, 

the more or less constant percentage of the blood tyrosine in Cardnus maenas 

would support the view that tyrosine of the cuticle is derived from the blood. 

This is probable because if tyrosine is oxidized by tyrosinase in the blood to 

form dihydroxyphenols in the early stages of the moult cycle as a preliminary 

to tanning, in the later stages when there is no evidence of tanning, tyrosine 

as such may be transported to the cuticle to serve as a substrate for the formation 

of pigmented products. Such a condition might explain why the blood 

tyrosine remains always more or less constant although tanning is confined to 

a period just about the time of moulting. This is in contrast to what has been


observed in Sarcophaga where the tyrosine content of the blood varies, being 

almost absent in the young feeding larva, then gradually increasing in the 

maturing larva, and again decreasing, presumably as a result of its consumption 

during the hardening and darkening of the cuticle. This feature is probably 

related to the fact that both hardening and darkening of the cuticle takes 

place simultaneously, whereas in Carcinus tanning is followed by the development 

of pigment. 

Trim (1941) pointed out that a proportion of the tyrosine derivatives of the 

cuticle may be in the form of dihydroxyphenols. The occurrence of free 

dihydroxyphenols has been noted in the cuticles of various insects (Pryor, 

1940). Possibly such dihydroxyphenols are derivatives of tyrosine formed in 

excess of the requirements for tanning, and therefore not linked up with the 

protein constituents of the cuticle. In Carcinus histochemical tests show that 

dihydroxyphenols are transformed into melanin-like substances formed 

probably as a result of further oxidation. Support for this view is found in the 

observation of Verne (1923) that the chromogen which gives rise to the black 

pigmentation of the eyes, legs, and carapace of crabs is an amino-acid. 

It may be seen from the work of Pryor (1940), Fraenkel and Rudall (1947), 

and Dennell (1947 a) that in insects the polyphenol formed in the blood is 

probably deaminated before reaching the cuticle where it is oxidized to 

quinones. From the close correspondence of the process of tanning in 

Crustacea, a similar deamination of the blood phenol may take place there 

also. If so, the melanins formed in the cuticle are not to be regarded as arising 

from the deaminated blood phenol, as melanins contain the NH group. 

Keilin and Hartree (1936) observed that if tyrosine is deaminated and the 

products oxidized, the reaction never gives rise to melanins. Therefore it may 

be reasonable to conclude that where darkening is brought about by the 

formation of melanin-like substances, tyrosine derivatives are formed in the 

cuticle possibly by the transport of tyrosine as such to the cuticle where 

further oxidation results in the formation of pigmented products and the 

excess of tyrosine derivatives may occur as free dihydroxyphenols. In insects, 

since darkening and hardening of the cuticle occur together, both the oxidation 

of deaminated products of the blood phenol and the oxidation of the 

tyrosine of the cuticle taking place coincidentally, it may not appear obvious 

that the two processes give rise to different end-products. But in Carcinus 

it is found that the early and slight tanning of the cuticle is separated by an 

interval of time from the process in which tyrosine appearing in the cuticle 

is oxidized by the phenolase. The sequence of appearance of the tyrosine and 

oxidase, the dihydroxyphenols, and lastly the melanins make it possible to 

infer that pigmentation of the cuticle is a separate process though chemically 

not unrelated to the earlier tanning. 

As has been shown, hardening and darkening of the insect cuticle are due 

to the tanning action of quinones resulting from the oxidation of dihydroxyphenols 

formed in the blood and transported to the cuticle. Pryor and others 

(1947) observed that a most likely mode of participation of such dihydroxy-


phenols in the hardening of the cuticle is by enzymic oxidation followed by 

condensation of the oxidized material with the proteins of the cuticle so that 

stable cross-linked structures, in which the nitrogen of the amino-groups 

becomes directly attached to the aromatic nuclei, are formed. It is also observed 

that proteins tanned by quinones are dark in colour (Pryor, 1948). From this 

circumstance it seems to have been inferred that the darkening of the cuticle 

is only incidental to that hardening process, being its natural consequence. 

Wigglesworth (1948 b), however, observed that the 'coloration of the tanned 

cuticles may be due to the presence of chromatophore groups such as the 

quinonoid group in the molecule or it may be due to coloured by-products 

arising from the oxidation of phenols not attached to any protein chain'. 

Such a view is consistent with the findings recorded in this paper, for it 

contemplates the occurrence of two processes, one primarily if not solely 

leading to hardening and the other contributing to pigmentation. Since 

phenolic substances are the materials involved in both processes, they appear • 

to be related though separated in point of time. Wigglesworth believes that 

some undeaminated tyrosine in the cuticle probably serves for melanin formation. 

It is interesting also to note that Fraenkel and Rudall (1947) in their 

study of the structure of insect cuticles observe that there may be a degree of 

protein tanning by deaminated tyrosine as well as formation of melanin from 

undeaminated tyrosine. That tyrosine as such may pass into the cuticle is 

supported by the observation that in Sarcophaga (Dennell, 1946) tyrosine is 

indicated in the presumptive exocuticle and is used up during puparium formation 

as seen by the fall of tyrosine content of the cuticle from 35 to 20 per 

cent. (Trim, 1941). This represents only a fraction of the total tyrosine consumption 

as indicated by the fall in tyrosine content of the whole organism 

from 1 -7 to 087 per cent. It is possible that the cuticular tyrosine contributes 

directly to melanin formation and may not take part in tanning of the cuticle. 

The observations made in Carcinus maenas support this view. 

The presence of melanins in insect cuticles has long been recognized. 

Gessard (1904) and Gortner (1911a, 1911&) have shown that the colouring 

of the insect cuticle is a fermentative process involving tyrosine and tyrosinase 

of the blood, dihydroxyphenylalanine being an intermediary product 

in the formation of melanins. With the revival of interest in the subject of the 

hardening of the insect cuticle as a result of the work of Pryor (1940) it has 

been shown that hardening is an enzymatic process very similar to that noted 

by Gortner and others, and so hardening and darkening have been regarded 

by some as two aspects of the same physico-chemical phenomenon. From the 

observations in Carcinus recorded here, phenolic hardening and darkening 

appear to be separate processes although the mechanisms underlying the two 

processes are similar. In insects this separateness is obscured, as in Sarcophaga, 

where tyrosine, although it accumulates in the cuticle before hardening, 

was not recognized as a pigment precursor; but a suggestion that they may be 

independent processes is gleaned from the work of Dennell (1947 a), who 

observed that the 'first sign of darkening of the cuticle is seen actually before


pupal contraction begins' and presumably before the hardening of the cuticle 

has commenced. He pointed out that the 'occurrence of darkening before as 

well as after pupal contraction gives an indication that the colouring of the 

cuticle and the muscular contraction which shapes the puparium are independent 

events although both are presumably induced by the liberation of 

the pupal hormone'. 

ACKNOWLEDGEMENTS 

I have great pleasure in acknowledging my indebtedness to Professor R. 

Dennell for help and guidance given me in the course of this study. I am 

grateful also to Professor *H. Graham Cannon, F.R.S., for his continued 

interest in the work. My thanks are due to the Government of Madras for the 

award of an overseas scholarship during the tenure of which this study was 

made. 

REFERENCES 

DENNELL, R., 1946. Proc. Roy. Soc. B, 133, 348. 

1947 a. Ibid., 134, 79. 

1947*. Ibid., 134,485. 

DRACH, P., 1939. Ann. Inst. Oceanogr. Monaco, 19, 103. 

FEIGL, F., 1947. Qualitative analysis by spot tests. New York (Elsevier). 

FRAENKEL, G., and RUDALL, K. M., 1940. Proc. Roy. Soc. B, 129, 1. 

1947- Ibid., 134, in. 

GESSARD, C, 1904. C. R. Acad. Sci., Paris, 139, 644. 

GORTNER, R. A., 1911 a. J. biol. Chem., 10, 89. 

1911 b. Amer. Nat., 45, 745. 

KEILIN, D., and HARTREE, E. G., 1936. Proc. Roy. Soc. B, 119, 114. 

LISON, L., 1936. Histochimie animate. Paris (Gauthier-Villars). 

PINHEY, K. G., 1930. J. exp. Biol., 7, 19. 

PRYOR, M. G. M., 1940. Proc. Roy. Soc. B, 128, 393. 

1948. Proc. Roy. Ent. Soc. Lond. A, 23, 96. 

, RUSSELL, P. B., and TODD, A. R., 1947. Nature, Lond., 159, 399. 

TRIM, A. R., 1941. Biochem. J., 35, 1088. 

VERNE, J., 1 1923. Arch, de Morph. Gen. et Exp., Fasc. 16. 

WIGGLESWORTH, V. B., 1947. Proc. Roy. Soc. B, 134, 163. 

1948 a. Quart. J. micr. Sci., 89, 197. 

1948 b. Biol. Rev., 23, 408. 

YONGE, C. M., 193Z. Proc. Roy. Soc. B, m, 298. 

1 Original not seen.

Phenolic Tanning and Pigmentation of the Cuticle in Carcinus maenas

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