IN DAPHNIA, AND OF THE STEUCTHRE OF THE EPHIPPIUM. 
89 
ratus. The ordinary eggs appear to die if any accident happens to the specimen in 
whose receptacle they are situated, and are certainly unable to withstand the influence 
of drought, or of great heat or cold. As the species of this genus are very often found 
in shallow ponds, which are liable to dry up, or to be entirely frozen, the species would, 
but for this provision, be often exterminated, in localities usually very favourable to them. 
An instance of this occurred to me. 
The 30th of July was so hot that it killed all the Daphnias which were in glass outside 
my window, and exposed to the sun. At the same time Cyclops quadricornis and Cypris 
awrantia were imhurt. I took some of the ephippia, and in a few days had the satisfac- 
tion of finding that some specimens were hatched. 
I now pass to the development of the agamic eggs. They are produced in BapJmia 
much more frequently than the ephippial eggs, and I have throughout this paper called 
them agamic eggs, because, as has long been known, they are remarkable for possessing 
the power of development without actual impregnation. Almost any amount of evidence 
might be given on this point. Throughout this summer I have had several females iso- 
lated in tumblers, which nevertheless have produced, by the intervention of these eggs, 
an uninterrupted series of young, 
Steauss* says, “ Sch^ffee est le premier qui est reconnu dans ces animaux la faculte 
qu’ils ont de produire plusieurs generations successives sans accouplement. II les a 
observes jusqua la quatrieme inclusivement. M. de Jiiehste les a suivis jusqu a la sixieme 
dans la D. pulex, et pense que chez d’autres elle pent aller jusqua la quinzieme.” 
Dr, Baied also, in his very useful ‘ History of British Entomostraca ’ (p. 79), has summed 
up the evidence of precechng authors, and appended some equally conclusive observations 
of his ovm. 
The usual appearance of the ovaiy immediately after the deposition of the eggs has 
been already described, and is figured in Plate VI. fig. I. Sometimes, however, the ovarian 
masses can be only here and there, and indistinctly, seen, and the ovary appears to be 
chiefly occupied by the cells, some of which afterwards become the germinal vesicles. 
Gradually, however, the walls of the ovarian masses appear, and generally the brown 
darkening (c), already described as the incipient condition of the ephippial egg, occupies 
one of the most, if not the most posterior. 
In such cases the development of the ordinary eggs begins while the brown darkening 
is in its most conspicuous condition, and before it has begun to fade away. Where there 
is no brown darkening, I have usually found the first signs of development to appear 
from twelve to forty-eight hours after the preceding “ laying.” In the few cases, how- 
ever, in which, after this act, the ovary could not be seen, no trace of it reappeared, and 
the animals died in three or four days. 
The place in the ovary at which the agamic eggs arise seems to be quite indeterminate : 
when there is an ephippial egg begun they may be anywhere in front of it, and in some 
* Loc. cit. p. 390. 
