112 TAGE SKOGSBERG 



R. WOLTERECK contests both these views in his work quoted above. The reasons 

 that seem, in the opinion of this writer, to controvert the explanation of these processes 

 as buoyancy organs are as follows (pp. 485 and 486): 



1) A number of the extremely developed processes, e. g. the crest in Hyalodaphnia, 

 the horns in Bosmina, are carried during swimming more or less vertically, i. e. they do not 

 contribute or contribute only very slightly by tlieir position to increase the horizontal 

 cross-section of the organism. 



2) Such processes in animals with variable energy of motion and variable specific gravity 

 can scarcely be explained as arrangements merely for increasing the power of buoyancy unless 

 they are extensive, because otherwise their importance compared with the two former factors 

 is too slight to be decisive. 



3) The main argument in favour of the buoyancy function, namely the temporal variation 

 in Hyalodaphnia, is not absolute evidence for this explanation. It is true that the crest becomes 

 longer in summer, but this does not j>rove the function postulated, as the head often becomes 

 considerably shorter in the late summer water, which is often very warm. This corresponds 

 to the experiments carried out by WolterecK; in warm water a low crest can be obtained and 

 a high crest in cold water according to the intensity of the assimilation. 



4) Bosmina longirostris and B. (coregoni) longispina are characterized in many places 

 in summer by short and in winter by long processes, i. e. exactly the opposite of what one would 

 expect according to the principle of buoyancy (the viscosity of the water decreases, as we know, 

 with a rise in temperature). Woltereck carried these Bosmina from water with a temperature 

 of about 12" C to water of 25" C and gave them abimdant food; the anterior processes (first 

 antennae) in these experimental animals were very considerably shortened, almost 50%. 



In order to test whether the explanation of these processes as balance organs was correct 

 R. Woltereck carried out the following experiments: 



1) The long crest in DapJinia cucuUata was removed. The result of this was that the 

 animals got on the average a more vertical position, such as is characteristic for the short-crested 

 D a p h n i d s. A consequence of this was that the operated animals swam in more steeply 

 ascending courses. ,,No disturbance of the equilibrium, which must show itself in an unnatural 

 position and direction of movement, occurred after the loss of the crest. This conseqiiently has 

 not the function of rendering possible the retention of the typical Daphnid position, i. e. of 

 making up for (,ausbalancieren') an otherwise one-sided weight. On the contrary it has the 

 function of altering the typical Daphnid position (for the originally crestless forms) in a definite 

 way. Because of this we cannot explain it as a balance organ, although it influences the position 

 of the centre of gravity." The removal of the spina in these animals had, on the other hand, 

 no essential effect on the position of equilibrium; the motion of the operated animals became, 

 however, less straight. 



2) After the removal of the first antennae in Bosmina longirostris the motion of the 

 experimental animals was altered from being in a straiglit line to a continuous backward rotation. 

 „Die Storung beruht aber nicht in einer Verschiebung des Schwerpvmkts : operierte wie unope- 

 rierte Tiere sinken, wenn man sie betaubt oder totet, mit dem Rilcken nach imten." 



