8 R. TAJNDBERG, DEVELOPMENT OF THE DAPHNIDS. 



Hellich ^^) has on the strength of this characteristic founded 

 his species Dfvphma f/ibbosa (1. c. p. 29, tig. 5). The length of 

 the spine and its position have been raentioned above. The 

 abdominal processes are also changed. as is nnderstood from 

 the fig. 18 where these prooesses are sketched from a young 

 female with remaining spine. I have not found that the thorns 

 on the abdonien change in any verv conspicnous way, but the 

 arniature of the seta- on the abdominal olaws seems, as might 

 be expected. less developed than låter on, some of them being 

 stouter than the others (tig. 1')— 17). The shell is in yonng 

 stages not so strongly i-eticnlated, and we tind it covered with 

 short prickles, largest or at least most conspicuons on the 

 dorsal and ventral margins of the shell. where they gradnally 

 disappear. and they do s(j last of all from the spine. 



From this review of the literature it ean be seen. that 

 mv own observations do not contain any new facts. Several 

 investigators have noticed the same things before. But by a 

 mere accident — I admit it willingly, for it was not origi- 

 nallv m}' intention to make any special examination of the 

 Daphnids — 1 obtained an opportunity to study the matter 

 under very favourable circumstances, because it can hardly be 

 donbted. that all my specimens belong to one and the same 

 species. However rich the material may l)e. supposing it has 

 been collected partly from one place partly from another. 

 the investigator can never be sure of getting the series of 

 evolution (dear and complete. As soon as the tendency and 

 direction of the transformation during growth have been made 

 obvious, the thing is verv much simpliiied. and it becomes 

 comparatively easy to deeide, whether the authors have had 

 younger or older forras before them. The result appears the 

 more interesting .^iince, aeeording to my opinion, the neglect of 

 observing the changes of form during growth is the chief cause 

 of the confusion and doubt which exist with regard to the 

 distinction of species among the Daphnids. or, we might safely 

 say. araong the Cladocera in general. In the species belonging 

 to the Daphnia pulex-gTow'^ (the Hyalodaphnia-groxL^ will be 

 treated further on) it may probably be taken for granted, that 

 the transformation goes on in the same direction as is shown to 

 be the case with the form I have had before me, at least in 

 the majority of cases. Thus, b}^ investigations in the same 

 direction it may be ascertained whether a species is to be 



