Videnskabelige meddelelser

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Videnskabelige meddelelser

12

The respiration of the Hydrachnids has always been a complete

enigma. They ara in possession of spiracles but nobody has aver

saen them coma to tha surFace and thrust tha rostrum above tha

surface of the water. Van V 1 e e t, who has studied the respiratory

organs most thoroughly is of quite the same opinion. We hava

had Hydrachnids hare in the laboratory in thousands, but we hava

naver saen a single ona coma to the surface to take air. It is

indicated that respiratorically they may be contantad with respir-

ation through the skin. I shall not here go into details with regard

to the papers of Kramer 0875, 1877), H aller (1882), Saville

Kent (1911, p. 273) and van VI eet (1897, p. 32) all relating to

the organs of respiration. According to the explorations of the two

last named authors, they are closed in the adults; with regard to

nymphs we really do not know anything exactly (sae van VI eet,

1897, p. 27).

If I should hava pursued this matter I would have usad^ tha

following working theory, the bearing strength of which I now

hope others will prove. It is a well known faet that many of those

freshwater organisms, which are derived from land, utilise their

organs of respiration hydrostatically as well as respiratorically. Vast

airspaces in the interior of the body contribute to reduce the spec-

ific gravity, decrease the falling velocity and ease the motion in

the water strata. Now I could think that the Hydrachnids during

the second pupal stage for this once filled their tracheal system

with air from the intercellular rooms of the piants; in this stage

the spiracles ara opan but during tha moult they are closed again.

The air stored up in the tracheal system has mainly hydrostatical

importance the respiration mainly going on through the skin. A

more thorough exploration with regard to the relation between

animal and plant is necessary to confirm or weaken the theory.

As nymphs and in the second pupa stage the mites are almost

always frea-living or attached to water piants. Parasitism in these

stages is only known in some species of Aia.v which are parasites

in mussels.

In his introduction Piersig (p. 37) himself reports this faet

quite correctly. It has therefore surprised me that in the very

same work ha indicates for two different species Mideopsis orhi-

culnris (O. F. Muller (p. 267) and 0.r//.s- strigatns (O. F. Muller),

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