Videnskabelige meddelelser

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Videnskabelige meddelelser

11

With regard to the nympha stage we really know very little. It

is often regarded as very short ; on

the other hånd it is most prob-

able that many mites even hibernate in this stage, those mites

which are parasites upon aquatic insects hibernate as pearshaped

bodies upon the hosts, from which they are hatched as nymphs in

spring; more thorough explorations on this point are desirable.

Commonly the nymphs are wanting the outer sexual organs but

Koenike has for a few species {Oxus 1898, p. 262; Unionicola

1915, p. 309) shown, that the outer sexual organs of the adult

mite can be found developed behind those of the nymphs.

Piersig maintains that at the end of the nympha stage the

mites attach themselves to the water piants, moult, pass through a

second pupal stage from which the adult mite is hatched. How

this attachment really takes place Piersig has not examined; but

two of the most reliable authors Duges and Thon maintain that

they (Limnochares and Hydrachna) are attached by means of the

rosirum which pierces into the plant tissue. With regard to the

genus Limnochares I can confirm Duges' observation. From more

casual observations with regard to many other mites I have got

the impression, that the rostrum of these suspended mites was in

a much more intimate connection with the plant tissue than hi-

therto supposed.

I have made these observations more than twenty years ago.

In 1907— 1908 my friend Dr. Adam Bøving studied the respir-

ation of the Donaciinæ larvæ; the explorations were partly carried

on at my laboratory. As is well known these larvæ insert the last

pair of spiracles which are hook shaped into the waterplants and

use the air in the airrooms for their respiration ; later on I studied

quite the same process but upon other aquatic insects: the larva

of Mansonia (published 1918).

It is now a wellknown faet that the spiracles of the Hydrach-

nidæ are placed upon the rostrum the very same organ which at

all events in Limnochares and Hydrachna is pierced into the

very same airrooms from which the spiracles of the larvæ of Do-

naciinæ and Mansonia transformed into piercing organs draw the

air in the tracheal system of these larvæ. The thought has often

struck me : Why do not the Hydrachnids also use the air of these

intercellular rooms respiratorically ? These nymphs also sit with a

piercing organ provided with spiracles inserted into this tissue.

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