Videnskabelige meddelelser

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Videnskabelige meddelelser

15

that ihose Hydrachnids which are nearest allied to the Trombidi-

idæ in the larval stages seek the surface of the water or the

borders of the ponds wheras those Hydrachnids which differ mostly

from the Trombidiidæ as larvæ are wholly bound to the water.

Coincident with the transformation from terrestrial to aquatic mode

of Hfe goes the transformation of the Hmbs from creeping to swim-

ming organs of motion.

How long the development of the Hydrachnids normally lasts

we do not know; it is unknown whether a Hydrachnid has one

or more generations in a single year or whether a single gener-

ation uses more than one year for its development. In our lati-

tutes I suppose that most species use one single year for their

development. I do not think that Soars supposition (1905, p. 84)

that the meiamorphosis of a Hydrachnid normally takes three years

is correct.

Fam. Limnochciridæ.

Limnochares aquatica (L.).

It is Duges (1834, p. 159) who first gives a more thorough

communication relating to the parasitic stage of Limnochares. He

mentions that the larvæ immediately seek the surface of the water

and there try to fix themselves to the pond-skaters (Gerridæ); he

indicates especially Gerris laciistris. When they again drop otf the

legs are, in relation to the body, much shorter and they move

more slowly. The larvæ seek „quelque anfraxuosité des pierres

submergées, deviennent des nymphes immobiles et au bout de

quinze jours laissent éclore un fort petit Limnochares d'un rouge

éclatant."

Apart from Piersig (1900, p. 466) and Thon (1906, p. 29)

who State that the eggs are laid upon stones, roots etc, that they

have a common enveloping layer and that the young ones are

hatched in the course of four to five weeks, it seems that nobody

has examined the development more thoroughly. Piersig states

only that the pupal stage is to be found upon water piants.

Limnochares aquatica, which otherwise (T h o n 1906, p. 29) is

indicated as being rare, is in our country a very common mite; it

can be found in great numbers on the roots of very many waterplants.

Especially between the roots of the Sparganium ramosam

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