the excretory system of the stick insect, dixippus morosus

188 J. A. RAMSAY
these granules is calcium carbonate. The egg shells of phasmids are hardened with
calcium oxalate (Moscona, 1950). Since the inferior tubules with their dilatations
and granules are absent in the nymph and poorly developed in the male, and since
the granules appear to be reduced in quantity during fasting (egg production
continuing), it seems likely that they are a calcium reserve which can be drawn
upon to provide material for the egg shells.
(c) Appendices of the midgut. These tubules are narrower (c. 50/i) than the others
and are uniform throughout their length. There is a well-developed brush border
and the inner margin can be brought to focus (Fig. 3 c). It is perhaps less sharply
defined than the scalloped edge of the 'wabensaum' in Rhodnius (Wigglesworth,
1931ft), but more definite than the edge of the border as seen at the tip of the
superior tubule (Fig. 3 a). No granules have been seen in these tubules.
Wigglesworth has reported that in Rhodnius the normal histological appearance
of the tubules is not preserved in artificial media. The same is true of the tubules
of the stick insect in all artificial media as yet tested. A Ringer solution approximating
to haemolymph in composition has been prepared (Ramsay, 1955). Within
an hour or two after being placed in Ringer the walls of the tubules begin to lose
their characteristic bright appearance. The striations of the brush border become
fainter and the border eventually disintegrates. The appearance of the nuclei
changes with what appears to be the separation of a coagulum from a clear fluid
within the nuclear membrane (Fig. 3d). A space appears between the cells and the
basement membrane which is clearly visible only under these conditions, and after
5 or 6 hr. a disintegrating mass of cells fills the lumen. The contraction of the
muscular elements in the walls continues for some time longer.
Table 1. Relative quantities of mineral bases as percentage
of toted mineral base expressed in equivalents
Na
K
Ca
Mg
Privet
leaves
(1)
13
35
46
6
100
Nymph
faeces
(2)
9
33
Si
7
100
Adult
faeces
(3)
EXCHANGE OF MINERAL BASES
The insect takes in sodium, potassium, calcium and magnesium in the proportions
in which they are present in privet leaves (Table 1, col. 1), and should presumably
eliminate them in the same proportions. In the case of the nymph elimination is
entirely by way of the faeces, and it is found that in the faeces of the nymph the
four bases are present in much the same proportions as in the leaves (Table 1,
col. 2). In the case of the adult female the eggs constitute a second channel of
elimination. The rate of egg production is considerable and in terms of ash a somewhat
greater weight is eliminated as eggs than as faeces. It is difficult, however, to
11
66 8
15
100
Eggs
(4)
10
5
83 2
100