AND OF PRODUCTS OF METABOLISM. 309 



which the water remained unchanged, the rate of repro- 

 duction and the number of offspring in a brood was con- 

 siderably diminished. The third generation was pro- 

 duced about 22 days after the second, and the fourth 

 about 25 days after that, and then the breeding 

 stopped. In the vessels with frequently changed 

 water, the third to seventh generations were produced 

 at intervals of respectively 18, 14, 15, 16, and 26 

 days, and then for some unknown reason the families 

 died out. The confined volume of water had another 

 and even more remarkable effect, however, as it 

 caused a distinct shortening in the length of the spine 

 formed by the posterior prolongation of the cara- 

 pace. Thus in one series of observations it was reduced 

 from a length of 241 (relative to the carapace length 

 taken as 1000) in the parents to one of 171 in the off- 

 spring; and in another series from a length of 276 in 

 the parents to one of 249 in the children, and 185 in the 

 grandchildren. In this latter case, therefore, it would 

 seem as if the acquired character of shortened spine 

 was inherited. 



Warren attributes these remarkable effects to the ex- 

 cretory matter thrown off by the Daphnias into the 

 water. Also he concluded that this matter " may 

 feasibly be supposed to be particularly injurious to 

 Daphnia; for when the Daphnia are fast disappearing, 

 there may be a swarm of Ostracods or Copepods (still 

 living healthily in the water)." In fact Warren in- 

 clined to the view, already suggested by the author in 

 the case of Echinoids and other marine animals, that 

 water fouled by Daphnia " becomes specifically injuri- 

 ous to Daphnia." 



