14 R. LlNDBERrt, DEVELOPMENT OF THE DAPHNIDi?. 



JcRiNE. •'') LiLLJEBORG "^) and otheis ha ve proposed as the real 

 Daphtiia pulex. 



Of coiir.se it is of the greatest in terest to make out the 

 nature of the ontogenetic developmeiit of the genuine longi- 

 spine forms of the species of Dnplmia. whioh live .pelagic> 

 ill the lakes, i. e. IIiiulodai)hni(i. Diiring the summer of 1803 

 I spent a good deal of time on this qiiestion. Biit a siicessful 

 stndy of the transformation diiring the growth here is sub- 

 ject to greater difiiciilties than is the case with the forms 

 living in smaller sheets of water (ponds). From time to time 

 [ made oollections with a plankton-net. Hensen' <^' Apstein's 

 eonstruction. in the lake of Davern at Finspong. 



Even a species of this groiip can afford. I think, in- 

 stances of verv important transformations of age. I could 

 not, however. f»dlow the developraent so far as that of 

 Dfiphnia pulex. 



In the month of Jnly. the greater part of the specimens 

 of the forms approximating to H. Cederströmii Schödler had 

 the head formed just as is shown in the figs. 26 — 31. From 

 these tigs. it is evident that the shape of the head varies from 

 the raore semilunate, upward-curved one of figs. 29 — 31, to 

 that with a straighter upper outline of figs. 27 — 28. I regard 

 those to be young. which låter on change to the form of figs. 

 32 — 35, reminding one of H. Bcrolinensis and KahJheryensis 

 Schödler or f/alrata Särs. 1 just ha])pen to observe, that the 

 shape of the head has changed in this direction. In one spe- 

 eimen. drawn in the fig. 31, the futiire outline of the head is 

 conspieuous. From this it is evident that the form represented 

 in the figs. 32 — 3ö is developed from the first-mentioned one. 

 In the season July — August I only found these two stages, 

 but in a plankton-colleetion of the 20*'' of September most 

 of the specimens have a form like that of the figs. 36 — 39 and 

 might be Daplinia cristata Särs ^■^) p. 149. 



I could not prosecute my studies on the transformation 

 any further. but my observations have. as I see from a paper 

 just received by O. Zacharias, ^") been confirmed by his in- 

 vestigations in grosser Pioner See. His figures. Pl. I, fig. 1 a 

 and b. agree tolerably well with mine, Pl. II. figs. 27 — 31 and 



