Videnskabelige meddelelser

Videnskabelige meddelelser


specimens sitting as gallshaped excrescenses on the twigs. Un-

doubtedly the Hydrachnids laid their eggs in Alisiua. Some piants

were now planted in an aquarium and 10 Hydrachnids brought

into it A few hours later the egg-laying went on and with a lens

I tried to study the prooess at close quarters.

A mite gets hold of the stem of a leaf and pierces with the

mandibles an orifice in it. Then it inserts the rostrum in the hole

and forms the mine. The length of the mine is commonly identic

with that of the rostrum.

When it had made the mine in a downward direction it turned

round and continued it upwards. Then the vulva was pressed to

the orifice; an egg appeared and was then, as far as I could see,

with the rostrum pushed down in the mine; the mite continued

till the mine was full. The vulva was drawn out as a tap and

more than once I got the impression that it acted as an ovipositor.

Unfortunately I had at that time no binocular aquarium microscope

so that I am not quite sure upon my observations; a more thor-

ough study of the organ is wanting. During the process all the

eight legs were projected free in the water; the rostrum was often

free of the plant and was not used as an organ for attachment.

Probably the palps are used as such but it is not certain. For a

long time it was quite enigmatic to me how a globular body could

be attached so firmly to a cylindrical vertical directed one. Once

I took a stalk out of the water; the mite did not release its hold.

Now taking the mite between my fingers I partly got the impression

that it was glued to the stalk, partly that the mite was fastened

by means of the genital piates.

As is well known the significance of the genital piates has

been interpreted in very different ways; they have been regarded as

apparatuses by means of which the mites are sucked fast to the

substratum, as fastening for muscles and as sensitive organs. Pol-

lo oh (1898, p. 33) has rendered an exact account of these differ-

ing opinions. Furthermore he has shown for Hydrachna inermis,

Diplodontus despiciens and Hydrodroma dispar that small uni-

cellular glands open in the pores. They are equally well developed

in males and females. He supposes that there may possibly be a

relation (already observed by Kramer) between the number of

cutaneous glands and the number of pores in the genital piates, the

more cutaneous glands the fewer pores and vice versa. The real

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