ENT0M03TRACA OF MINNESOTA. 161 



The true place of the genus, as it appears to the writer, was hinted 

 at by Birge {J^otes on Cladocera). Monia seems to be the pivotal point 

 of the Cladocera, at least of the families above mentioned. Without 

 going into phylogenetic speculation, it is suggestive that this genus 

 can and does by preference live in very impure water, and may there- 

 fore have had an early origin. From Moina diverges the stem of the 

 Dajyhnidce by way of Geriodaphnia, Simocephalus and Daphnia. These 

 two latter genera are intimately connected by Simocephalus daphnoides 

 Herrick. . Scapholeberis is connected with Ceriodaphnia through S. an- 

 guUda Herrick. The Sldidce seem to diveege by the way of Daphnella, 

 through which by means of Fseudo-sida the genus Sida is reached, and 

 finally Limnosida, Latona and Holopedium. The relationships of the 

 curious Polyphemidw are less evident. 



The Lyncodaplmidce make an easy transition to the Lyncekls proper^ 

 while the Bosminidce are still quite isolated, but are suggested by 3Ia- 

 cy^othrix pa^iper. The fact that Moina stands thus related to radiating 

 groups is simply suggestive, but it is suggestive of its possible j^n- 

 tiquity 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 (Grobben '79). 



The genus is characterized by Weismann and Gruber ('80) about 

 as follows: 



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

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

 large, movable, furnished with a sensitive seta near the middle, flagel- 

 liform ; antennules of the male very large, hooked at the end. The 

 setse of the antennae are all ciliate; the tri- articulate ramus with five 

 setfe; posterior margin of the valves thicker in the median line; caudal 

 setse 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 originate 

 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 

 reolirostris; while in M. paradoxai\iQ summer eggs have yellow and the 

 winter set snow-white yolk. There are never more than two winter 

 eggs in any of the Daphnidm, but there are as many as twenty summer 

 eggs in some cases in Moina. In M. rectirostris only one winter egg is 



