Videnskabelige meddelelser

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Videnskabelige meddelelser

14

lores are lacking) or the whole nietamorphosis must be extremely

abbreviated the parasitic stage being dropped out. If I should have

continued this exploration I would in the short time from May to

June every fourth day have examined the whole fauna and flora

of these little ponds, many of these not being much larger than a

room in my laboratory. This I suppose is the best way to learn

the development of a series of our most common Hydrachnids.

It is rather difficult to understand whether Piersigs suppo-

sition that the larvæ can be parasites upon almost all aquatic insects

is commonly adopted; upon that point the litterature is remarkably

silent. As far as I know only Soar (1905, p. 84) maintains quite

the opposite supposition. He says: „No doubt each species has its

own particular host which it seeks and to which it attaches itself

as soon as possible." I really think that Soar carries the thing

too far but undoubtedly my views are nearer to Soar s than to

Piersig's interpretation. Another reason because of which I can

not follow the last named author is the following. In the nature

the Hydrachnids undoubtedly form certain relatively sharply defined

societies. Such societies are those of the running waters, that of

the ponds drying up in summer, that of the ponds rich in water

piants and that of the great lakes especially upon 4—7 m; atten-

tion may also be paid to a little peculiar semipelagic society of

which we momentarily know very little. Lundblad (1912, p. 21 6)

has also kept this matter in mind. This more constant occurrence

of certain species on quite distinct localities is according to my

idea mostly in accordance with the supposition that the Hydrach-

nids by no means are able to select their hosts so indiscriminately

as Piersig seems to suppose.

Recently Oudemans (1913, p. LXIII) has, according to a

short note, shown that he partakes of the view set forth by Soar

like myself. He says that the IJiuiiocluiriiuv mainly are parasites

upon Hijdrometridæ, the Eijhviniv upon aérial insects, the Ilijdrij-

phantimv likewise upon aérial insects mainly the Culicidæ, the

HydrachnirKV on the Dijliacs and the Xepidæ; all the Hygroba-

linæ are parasites upon aquatic insects and do not leave the ponds

in which they are hatched. His view is undoubtedly a progress

but, especially with regard to the Hygrobalinæ, it is too schematic

and incorrect for the genus Arrlwmirus. Oudemanns shows

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