FRESH-WATER ANIMALS 9' 



these cases the small free-swimming larva, or 

 nauplius, though very unlike the parent, is provided 

 with very powerful swimming appendages, and is 

 therefore able to hold its own against streams 

 which would be fatal to those small larvae which 

 depend for locomotion on the action of cilia. In 

 fact in these Entomostraca the mode of life of 

 larva and adult is the same, and hence if the adult 

 can hold its own, there is little reason why the 

 larva should not do so also. Still it is a point that 

 requires further investigation, how it comes about 

 that Daphnia should lay large eggs, while the 

 allied genera, Cyclops and Cypris, living under the 

 same conditions, and in the same ponds and streams, 

 produce very small eggs. 



Concerning these fresh- water Entomostraca there 

 is another point of much interest, that would well 

 repay further examination. In the sea there are 

 marked differences between the shore and shallow- 

 water animals living near to the land, and on the 

 other hand the oceanic or pelagic forms that are 

 met with in the open sea hundreds of miles from 

 land. The same distribution applies to the large 

 fresh- water lakes, in which shallow- water and 

 pelagic fauna may also be recognised. 



The pelagic forms are very generally character- 

 ised by the possession of eyes of unusual and often 

 of gigantic size, and by their habit of remaining 

 down at some depth during the daytime and only 

 coming to the surface at night. Professor Weis- 

 mann has suggested that these two peculiarities 

 may be associated together, in this way. Ordinary 



