10 Transactions of the Society. 
the differing theories, and suggest experiments which might, I think, 
decide between them. 
There are, as no doubt you are aware, three sorts of e""s among 
the Botifera, Of these the ordinary, or “ summer ” eggs, have only a 
soft membranous covering; they are hatched soon after they are 
laid, and are of two sexes, distinguished from each other by both shape 
and size. The female eggs are large and distinctly oval ; the male 
eggs are smaller and nearly spherical. The third sort of egg, or 
“ ephippial ” egg, has a double shell, often beset with spines, bosses, 
or prickles. It is sometimes termed a “ winter ” egg, but this is a 
misnomer, as it occurs at all times of the year. 
Now there is no doubt of the continued production of female eggs by 
parthenogenesis in every family of the j Rotifer a ; and indeed, among 
the Bdelloida no other mode of reproduction has as yet been seen : 
but concerning the origin of ephippial egss there is no such agree- 
ment. Cohn thinks that they are the product of sexual intercourse ; 
Huxley says that sexual intercourse gives rise to the ordinary soft- 
shelled eggs : Plate maintains that sexual intercourse has no effect 
in determining the sort of egg that is to be laid. Again, Plate 
declares that no female ever lays more than one sort of egg ; while 
Balbiani, on the contrary, says that the same individual may first 
lay ordinary female eggs and then ephippial eggs. 
It is not easy to steer one’s way through such contending autho- 
rities ; but before making the attempt, let us first separate the facts 
from the opinions. 
(1) It is admitted on all hands that virgin females will pro- 
duce virgin females, in unbroken succession, through many genera- 
tions. 
(2) Balbiani states that he has often observed, that a solitary female 
of Notommata Werneckii , inclosed in a gall of Voucher ia, has first 
laid ordinary female eggs, and then ephippial eggs : and that the laying 
of the latter was preceded by a gradual exhaustion of the vitality of 
the germ in the ordinary female egg, as shown by a great number 
of them remaining sterile ; or, if the embryo were formed, by its dying 
without hatching, even after the eye-spot had become visible. More- 
over, the males had nothing to do with the matter, as they were absent 
during the whole of the observations. 
(3) Huxley has observed in Lacinularia socialis that the ephippial 
egg is formed out of several germs and their surrounding yolk ; and I 
have myself watched the entire process of the formation of an ephippial 
egg in Conochilus volvox, and seen that it consisted of nearly two- 
thirds of the ovary, with many inclosed germs. 
(4) Plate has tried many experiments in coupling females (that 
had already begun to lay eggs) with males ; and in no case did sexual 
intercourse alter the kind of egg that the female had been in the 
habit of laying. 
(5) In two cases Plate observed the results of coitus on a young 
