Videnskabelige meddelelser

Videnskabelige meddelelser

a normal scheme for the view of the development. By this manner

of proceeding Piersig has put a stop to further investigations;

the naturalists having got the impression that science upon that

point has said its last word. The above named scheme is shortly

expressed as follows. All the hydrachnids deposit eggs; as far

as we know at present none bring forth their young ones alive.

1. The first stage is the egg stage. 2. As the development pro-

ceeds the firm outer membrane is ruptured and the embryo rests

in a more delicate inner membrane: This is the Deutovum stage

(Claparéde). 3. The third stage is the first larval stage, the

parasitic state, in which the mite has but three pairs of legs.

4. The fourth stage is the first pupal stage in which the larva

loses its power of locomotion and is rounded off in to the pear- or

ballshaped body. 5. The fifth stage is the nymph stage or second

larval stage. The mite has now four pairs of legs but still lacks

the perfect development of the sexual apparatus. 6. The sixth

stage is the second pupal stage in which the mite again loses its

power of locomotion. 7. From the sixth stage develops finally the

adult mite.

From many pages in Piersig's Work (f. inst. p. 79, 80, 91, 96,

100, 107. 161, 175, 190, 240, 245, 26H a. o.) it can be pointed

out that the opinion of Piersig relating to the development of

water-mites is as follows.

Piersig takes for granted that the parasitic stage is completed

upon insects living their whole life in water; further that the choice

of host is to the mite a matter of entire indifference. Only with

some verbal variation Piersig's report with regard to the para-

sitism of the different species restricts itself to the following short

remark: „Schmarotzt an Wasserinsekten" or „schmarotzt an Wasser-

kaferlarven". The last information is indeed very remarkable. The

only larvæ of water beetles upon which the mites really could be

parasitic are as far as I can understand those of Hydrophilidæ

and Dytiscidæ. Now the litterature shows no examples of para-

sitism on larvæ of these families. During my study of these be-

ings I have caught thousands of them and for years have had

them in my aquaria. I have never yet seen a single larva of mite

on any of them. That Piersig himself should have made any

observation with regard to larvæ of mites upon larvæ of Hydro-

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