Videnskabelige meddelelser

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Videnskabelige meddelelser

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the Hydrachnids clearly pointed out. 1. Eggstage and the form-

ation of the deutovum 2. The development in the deutovum.

3. The first larval stage. 4. The first pupa stage and the form-

ation of the second larval stage (the nymph). 5. The develop-

ment of the fullgrown mite. Claparéde does not separate a spec-

ial second pupa stage which otherwise seems to be a rule for the

Hydrachnids (the stage attached to water piants). It can however

from his text (p. 464) be seen that he has seen and apprehended

it as such. He shows that A. Bonzi in all its stages is parasitic;

that the egglaying takes place at all seasons; that the mite in the

first larval stage is very active but that this stage is very short.

The first stage is carried on in the mantle cavity; after this stage

the larva bores itself into the gills. Here it passes into the pupa

stage and loses the power of locomotion. Also this nymph stage

lasts only a short time; the mite is again deprived of its power

of motion and after the second pupa stage it is again to be found

in the mantle cavity of the host. Apart from A. crassipes, which

will be mentioned later on, the knowledge of the biology of the

Aia.v species is not augmented until 1899. Piersig mentions 7

species but from the te.xt it may be supposed that the biology of

A. figiiralis C. L. Koch, aculentus Koenike and triciispis Koenike

is unknown. The three species .4. ypsilophoriis (Bonz), Bonzi

Claparéde and interinediiis Koenike are all decided parasites which

at any rate only as nymphs and probably only for a very short

time, are free living.

The paper of Wolcott (1899, p. 193) on the North American

species augmented the knowledge of the biology in a very high

degree. The Ala.v species do not occur in Unionidæ only but

also in the South American Ampullaria species and in Sphæriuin

(Koenike). From an examination of nearly 3500 mussels Wolcott

has found 13 species. The most interesting new facts which the

investigation has brought forth are the following. The eggs are

laid singly in the mantle and the gills, only by .4. ingens Koen.

in small heaps between the gills. The spines guarding the genital

opening probably assist in oviposition. In the case of the Unio-

dwellers the eggs are more abundantly deposited in the gills, by

the A/jOf/on/aparasites more numerously in the mantle. The first

two stages are passed in the substance of the gill, the first larval

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