Videnskabelige meddelelser

Videnskabelige meddelelser


It will now be understood that we really know very little with

regard to the development of Hijitrachna-species. Owing to Du-

ges' explorations we know that of H. globosa best but also with

regard to this further observations are necessary. It is rather prob-

able that by no means all the Hijdrachnn species develop in

quite the same manner. Whilst //. (jlobosa is hatched from the

wellknown pearshaped bodies on Dijtiscids and waterbugs H. geo-

(/raphica is said to be hatched from the large sacs below the

elytræ of Dijtiscids (Pi er si g, 1900, p. 441) but also this indic-

ation can not be regarded as an established faet.

H. Williamsoni Soar.

In the years 1911 and \9\ 2 studylng Dijtiscidæ, Hijdrophilidæ

and Odonata I often came to a little peculiar lake Hjortesø, abt. 3

km from Hillerød. A day when I threw my net amongst some

Alisma plantngo piants I caught very many specimens of pro-

bably one or two HgdracIina-spec\QS. The one of them was H.

geographico, the other was quite new tome. Mag. L. Pederse n

has kindly determined the species to H. Willianisoni Soar; they

were red, but of a peculiar dark colour. Looking at the Alisma-

plants I now saw, that the Hydrachna in great numbers swam be-

tween the piants. In a few minutes many of them had again fastened

themselves to the twigs; undoubtedly I had disturbed them by

throwing my net. Unfamiliar with the hydrachnological litterature

I now had occasion to observe a phenomenon, which was quite

unknown to me. Taking a plant in my hånd I saw that the twigs

of Alisma were furnished with many hundreds of small galleries

running just below the epidermis.

mm long, but some were

Most of them were only 2 — 3

1 — 2 cm or a little more. The width

was only V 2 mm. In the middle of the shorter mines was an ori-

fice, in the longer two. From the outmost limits of the mine and

to the orifice there was commonly not beyond 1--' g mm; on the

very long mines the distance might however be longer. In the

mine the eggs were arranged in one or two rows. The eggs were

red and undoubtedly eggs of Hydrachnids. The number of eggs

in a mine was commonly 10-30. All the mines were parallel to

each other and all stretched exactly in the longitudinal direction of

the twig. Already by looking at the piants in the pond I saw many

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