Videnskabelige meddelelser

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Videnskabelige meddelelser

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In this stage tlie larvæ have ahvays preserved their power of

movement. Some of the mites were loosened from their hold and

brought into a jar with waterplants, others into a jar with ^vater

but without piants; the larvæ were all able to swim but fastened

themselves when occasion was given them as soon as possible on

waterplants. Those from 16 VIII had already 20 'VIII broken out

of the sixlegged larva-skin and now swam as nymphs round in

the water; the old skin is fastened to the plant and with a lens

it can be observed that they are fastened by means of the rostrum.

Also those larvæ which have had no occasion to fasten themselves

to waterplants are able of encystment ; but as far as I have seen

many of them never give nymphs being covered with Mucoraceæ.

It seems as if the Zijgopteridæ most probably are infested in

July; from the first day in September I have never found Z;/(yo/;-

teridcv with larvæ.

I have in the foregoing pages tried to gather all what we know

at the present time with regard to the metamorphosis of the Hy-

drachnids. Here and there I have been able to add some new^

facts to what was hitherto known. At the first glance it seems

Strange enough that our knowledge of the metamorphosis of these

charming little creatures is so trifling as it really is. By a closer

consideration this will be easily understood as these studies claim

so much intense reflection, a great outer apparatus, and unlimited

time for explorations. The difficulty is not only to keep the mites

and their larvæ alive; the most troublesome is that the explorer

also must keep the hosts of the larvæ alive. It is necessary to

hibernate Dytiscs and Hydrocores in aquaria and keep Odonata,

Perlidæ, Culicidæ and Chironomidæ living for weeks and often for

months. Every entomologis! knows that this is a very difficult thing.

It is necessary constantly to be in contact with nature itself and

at every moment change the basis of observation from nature to

the laboratory or vice versa ; try to catch hold of a thread here and

pursue it further there. The explorations may be carried on over

more than one year. The first year the investigator nearly always

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