Videnskabelige meddelelser

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Videnskabelige meddelelser

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stage. Later on I saw that Thon (1906. p. 44) confirms this last

view. He says to wit that the eight legged nymph stage „auf den

Hydrocoriden ihre Metamorphose vollenden". Still it must be re-

niembered that all the authors agree that the nymphs and imagines

of Eylivis are much alike and that, therefore, a mistake is possible.

20 I\^ 1912 I had the good fortune in one of the Donse ponds

North Zealand to make another remarkable observation. Along the

sunny shores of the little lake I found the rather rare little Dytisc

Grophoderes bilineafiis Degeer in great numbers. On one of the

specimens I saw, that there was something wrong with the wing-

covers and by looking further I found a large red Hydrachnid

parasite behind them ;

this little discovery was of inlerest. because

under the wingcovers of the Dytiscidæ, as far as I know from

litterature, we have hitherto only found these large parasitic stages

on the genus Dytiscus. The lake has very many small bays and

trying in these different small ones I saw that in some of them

more than 70 '^^/o of the Graplwderes were infested, in others were

only very few. A good deal Dytiscs were immediately brought into

niy aquaria. 1 V I was again at Donse pond. Graphoderes was

now rather scarce ; in the little bay where 20 IV in a few min-

utes, I gathered about 100 specimens, I could now only with great

difficulty find 60 and of these specimens only 4 had parasites.

Some of the specimens in the aquaria died, but in the time from

1 V to 13 V some of the nymphs were hatched ; these nymphs

all belonged to the genus Eijlæis; they lived in my aquaria for

three weeks and never anchored themselves to the waterplants

and, though there was food in abundance, did not grow larger

during this time. Also in this case I am not fully convinced that

I did not have fullgrown mites before me.

A good deal of the material was preserved ;

a more thorough

examination showed, that the parasitic stages almost all were of the

same size ; all were broad, flattened sacks without any trace of

legs; they were often narrowed in the forepart and were but

slightly fastened to the host. In many of the sacks the full grown

stages were very conspicuous. Most of the parasites were fastened

to the abdomen below the elytra, but many of them on the under-

side of the wingcovers; these often carried two, in a single case

even five parasites on the same specimen. For me it is rather

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