iv SCHMANKEWITSCH'S EXPERIMENTS 215 



species which are often based on characters such as 

 those which Schmankewitsch refers to. These are 

 specific characters, or at least we are told so every 

 day by any number of systematic zoologists, and they 

 are supposed to know " all about species," so we may 

 go on with the quotation. " Besides the differences 

 observed in the antennae of the salt-water generations 

 of Moina rectirostris, our attention is called to the 

 number of slender finely-toothed spines which occur 

 on the lateral surface of the post-abdomen of Daphnia 

 rectirostris, running in lateral series and nearly parallel 

 with the direction of the rectum. Leydig called them 

 finely-feathered spines, which I would have called 

 triangular laterally dentate plates. However this 

 may be, we observe in our fresh-water forms of 

 D. rectirostris on each side from eleven to thirteen of 

 these spines or plates, and only from seven to nine 

 in the salt-lake form, meaning here, as a matter of 

 course, mature individuals only. In younger specimens 

 there are fewer spines than in the adults of the same 

 surroundings, and therefore the young fresh-water 

 forms have the same number of spines at a certain 

 age as the adult forms of the salt lake, which demon- 

 strates the retarded development of the latter." And 

 further on : " We now find, in comparing the fresh- 

 water generations with the salt-water generations of 

 Daphnia rectirostris, that the latter generations are 



