BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 20. AFD. IV. N:0 2. 15 



36 — o9, and he has probably studied the same species. He 

 Avas able to follow the transformation right on to December 

 and found tliat the head then aequires an evenly rounded 

 shape, Pl. I, fig. le, der die Species ganz unkenntlich machen 

 wilrde, wenn man nicht alle Uebergänge, die von der langen 

 nach oben gebogenen Kopfform allmählich zu der rnnden hinge- 

 fiihrt haben, wii'klich gesehen hätte^. Besides, he fonnd in 

 another lake in the neighbourhood. that the spine of Hyalo- 

 (laphnia Berolmensis Schödler grows shorter in the aiitumn. 



Bnt he regards these change.s as Saisonformen > or varia- 

 tions produoed by vaiious exteriör influences at different 

 times, not as transformations depending upon growth. loc. cit. 

 p. 121. So iirmly established is the opinion that the sexually 

 ripe forms can not alter in time of growth. Moreover. the 

 discovery of these season-forms» does not seem to have di- 

 stnrbed his ovvn faith, that the species established by Särs, 

 Schödler and other investigators are well defined. 



My researches have not been extensive enongh to allow 

 me to enter into a more minnte eriticism of these species, but 

 from my own discoveries and from those of Zacharias it ought 

 to be evident that the explanation I have given above is 

 (jnite eorrect: the Daphnids (and Cladocera in general) undergo 

 very great transformations dnring growth, and an inquiry 

 into and a revision of the species of the Daphnids and of the 

 Cladocera in general is highly desirable. * 



From my researches and those made by Zacharias it is 

 obvious that all transformations of the Daphnid.s tend in the 

 same direction, i. e. spines and (jther prominences, the so-called 

 balancing organs, tend to become shortened or even to dis- 

 appear in time, as is the case with the larval forms of other 

 Crnstacean orders. There is no donbt, that these chai\ges 

 dnring the growth are adapted to the surroiinding con- 

 ditions of the medinm in which they live, and that they 

 are of a certain advantage for the animals. In this respect it 

 seems to be of great importance to stndy their bathymetrical 

 distribiition and its connection with the changes of tempera- 

 ture in the water at ditierent seasons. Forel-^) has called 

 attention to the importance of the temperatnre in estima- 



* Zacharias says that similar changes occur even in the genus Bosmina 

 and in the same direction, for the balancing organs, viz. the long antennae, 

 are shortened. 



