644 On some Entomostraca of Lake Michigan [August, 



The difference of reproductive energy, as shown by the much 

 smaller egg-masses borne by the lacustrine species, depends upon 

 the vastly greater destruction to which the paludinal Crustacea 

 are subjected. Many of the latter occupy waters liable to be 

 exhausted by drought, with a consequent enormous waste of ento- 

 mostracan life. The opportunity for reproduction is here greatly 

 limited — in some situations to early spring alone — and the chances 

 for destruction of the summer eggs in the dry and often dusty 

 soil are so numerous that only the most prolific species can 

 maintain themselves under such conditions. 



Further, the marshes and shallower lakes are the favorite 

 breeding grounds of fishes, which migrate to them in spawning 

 time, if possible, and it is from the entomostraca found here that 

 most young fishes get their earliest food supplies— a danger from 

 which the deep-water species are measurably free. Not only is 

 a high reproductive power therefore rendered unnecessary among 

 the latter by their freedom from many dangers to which the shal- 

 low-water species are exposed, but in view of the relatively small 

 amount of food available for them, a high rate of multiplication 

 would be a positive injury, and could result only in wholesale 





EXPLANATION OF PLATE IX. 



i.—O.sphranti 



cum labronectum, second max 



Wiped, x 





mandible ar 



id palpus, ; 







4— Osphrantu 



:um labronectum, tf, antenna 



; X 38. 



5— 



tf, P«t of 









6._Cyclops in 



rectus, tf, X 38. 





7 — Osphranti. 



:um labronectum, leg of fourt 





8.— Epischura 



lacustris, J», X 42. (Some 







M are concealed. The segmentation of 





pletely shown. See text.) 





9— Osphrantii 



:um labronect-m antenaula 





10.— Cyclops thomasi, leg of fifth pair. 







" ?.X38. 





12.— Holopedh 



imgibberum, 9. 







" abdomen and fu 





14.— 



" marking of shel 







eye and macula 



nigra. 



16.— Cyclops tl 







17— Bosmina ( 



after Gerstaecker). 





