ENTOMOSTRACA OF MINNESOTA. 161 
The true place of the genus, as it appears to the writer, was hinted 
at by Birge (Votes on Cladocera). Monia seems to be the pivotal point 
of the Claducera, 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 
Daphnide by way of Ceriodaphnia, Simocephalus and Daphnia. These 
two latter genera are intimately connected by Simocephalus daphnoides 
Herrick. Scapholeberis is connected with Ceriodaphnia through 8S. an- 
gulata Herrick. The Sidide seem to diveege by the way of Daphnella, 
through which by means of Pseudo-sida the genus S/da is reached, and 
finally Limnosida, Latona and Holopedium. The relationships of the 
curious Polyphemide are less evident. 
The Lyncodaphnide make an easy transition to the Lynceids proper, 
while the Bosminide are still quite isolated, but are suggested by Ma- 
crothrix pauper. The fact that Moina stands thus related to radiating 
groups is simply suggestive, but it is suggestive of its possible an- 
tiquity and synthetic character. casera 
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 
sete of the antenne are all ciliate; the tri-articulate ramus with five 
setze; posterior margin of the valves thicker in the median line; caudal 
sete 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 
rectirostris; while in M. paradoxa the summer eggs have yellow and the 
winter set snow-white yolk. There are never more than two winter 
eggs in any of the Daphnide, but there are as many as twenty summer 
eggs in some cases in Moina. In WM. rectirostris only one winter egg is 
