514 
G. H. GEOSVENOR AND GEOFFREY SMITH. 
In fact, as Weismann pointed out, there is only one gene- 
ration which invariably and uniformly consists of partheno- 
genetic females, viz. the first generation which hatches out 
from the resting eggs. Any of the succeeding generations 
produced partheuogenetically may consist of males and 
ephippial females as well as of parthenogenetic females, but 
that they invariably are so constituted is negatived by our 
experiments. 
The ephippial or sexual females and their relation to the 
parthenogenetic females demand a word of explanation. The 
two kinds of female do not differ from one another structu- 
rally at first, but a young female that is destined to produce 
a resting egg and ephippium can be soon recognised by the 
greater opacity of the ovary, and later by the presence of the 
large I’esting egg in the ovary. At most two such resting 
eggs are brought to maturity and deposited in the specially 
prepared brood-pouch or ephippium, where they may be 
seen as opacpie dark-red bodies of very large size. The 
ordinary eggs of the parthenogenetic female are, on the other 
hand, very numerous, small, and of a transparent greenish 
colour. Now, as the result of onr observations, it is found that 
an ephippial female, if it is not fertilisedby amale, may i-eabsorb 
its resting eggs and turn into a parthenogenetic female later. 
But we did not findany caseof afemalethat had produced eggs 
parthenogenetically turning into an ephippial female, and 
giving rise to resting eggs. This is in agreement with Weis- 
manu’s observations on Cladocera in general, Issakowitsch (2) 
being the only observer who records the contrary in the case 
of Simocephalus vet ulus. 
In the tables given on p. 521, 522, no mention is made of 
the occurrence of ephippial females, because it was im- 
practicable to include them by the methods necessary for 
dealing with such large numbers of individuals, owing to the 
necessity of keeping the females alive for some time in order 
to determine whether they were ephippial or not. Neverthe- 
less this was done in a large number of cases, and it was 
found that ephippial females occurred in the same broods in 
