STATE GEOLOGIST. 33 



The Lyncodaphaidse make an easy traasition to the Lynceids 

 proper, while the Bosminidse are still quite isolated, but are sug- 

 gested by Macrothrix pauper. The fact that Moina stands thus 

 related to radiating groups is simply suggestive, but it is sugges- 

 tive of its possible antiquity and synthetic character. 



The three species of this genus stand very poorly distinguished 

 from one another and their specific validity may be doubted. 



The most exhaustive study of the embryology of the Cladocera 

 was based on Moina. {Grohben, Entwick d. Moina, etc.) 



The genus is characterized by Weismaun and Gruber^ about as 

 follows: 



Head prone; separated by a depression from the thorax; fornices 

 obscure; rostrum none; pigment fleck absent; antennules of the 

 female large, moveable, furnished with a sensitive seta near the 

 middle, flagelliform; antennules of the male very large, hooked at 

 the end. The setae of the antennae are all ciliate; the tri-articu- 

 late ramus with five setae; posterior margin of the valves thicker 

 in the median line; caudal setae very large, about twice in the 

 length of the animal; anus above the claws; feet of the first pair of 

 the male with a strong hook. 



Weismann has shown that both summer and winter eggs origi- 

 nate from groups of four cells, one of which only is transformed 

 into the egg, the remaining three serving simply as a supply of 

 nourishment for the egg, which absorbs it directly. Both eggs and 

 nutrient cells develop from the epithelium of the termination of 

 the ovary. The summer eggs have less yolk than the winter brood, 

 and the yolk is bluish in the summer eggs and deep red in the 

 winter eggs of Moina rectirostris; while in M. paradoxa the sum- 

 mer eggs have yellow and the winter set snow-white yolk. There 

 are never more than two winter-eggs in any of the Daphnidge, but 

 there are as many as twenty summer eggs in some cases in Moina. 

 In M. rectirostris only one winter egg is produced, which is one of 

 the best distinctions of the species, as this is, perhaps, the only case. 

 {Naturgeschichte der Daphnoiden, Weismann.) The first genera- 

 tion, springing from the winter eggs (impregnated eggs), is com- 

 posed solely of females which reproduce parthenogenetically; the 

 second brood contains sexual males and females, thus completing 

 the cyclus. 



1 Ueber einege netie Oder unvolkommen gekannte Daphniden, Freiburg, 1877. 

 3 



