1898] REPRODUCTION OF THE ROTIFERA 45 
male Asplanchna “ attached to the side of the female,” and though 
Dalrymple refers to the “intromission of the male organ into the 
vaginal canal,” it would appear that this was rather an inference 
than an observation. Gosse however observed and described the 
process of impregnation by the cloaca in Brachionus. Cohn (6) 
observed in Hydatina the males adhering to any part of the body of 
the females. He found spermatozoa in the body-cavity of the latter, 
and recognizing the improbability of their having reached that 
position by way of the cloaca, he was led to suspect the existence of 
a special copulatory pore in the region of the neck. He was unable, 
however, to demonstrate any such aperture. In 1885, Plate (12), 
investigating the same species, stated that impregnation took place 
by the penis of the male perforating at any point the body-wall of 
the female and injecting the spermatozoa into the body-cavity. <A 
similar process had previously been described by Lang (11) in 
certain Polyclad Turbellarians ; and it is now known to occur in 
several other groups of ‘ worms,’ notably in certain Hirudinea where 
it has been investigated by Whitman (20). The last-named writer 
names the phenomenon “ hypodermic impregnation,” and gives a full 
summary of previous observations on its occurrence in other groups.’ 
M‘Murrich has since adduced evidence to show that it occurs even 
in certain Isopod Crustacea. Plate’s account, though doubted by so 
great an authority on the Rotifera as Dr Hudson, has been confirmed 
by Maupas, whose important researches will be referred to below. 
It is not yet clear, however, in what way the unarmed penis of the 
male can perforate the tolerably resistant cuticle of the female; nor 
can it be doubted that hypodermic impregnation is by no means 
universal among the Rotifera, for cloacal coition has been seen by 
many observers, and has been figured by Weber (15) in Daglena 
catellina. 
In several species, Ehrenberg described, besides the more usual 
thin-shelled ‘ summer’ eggs, thick-shelled ‘ winter’ eggs, which only 
hatched after a long resting-period. Huxley, studying these in 
Lacinularia (5), applied to them the name ‘ephippial’ eggs 
on the analogy of the similar structures so named among the 
Cladocera. He, however, fell into the error of regarding them 
as multicellular buds like the ‘ gemmules’ of sponges or the ‘ stato- 
blasts’ of Polyzoa. Cohn was the first to offer what has since been 
the generally accepted interpretation of these two kinds of eggs. 
He observed that the production of ‘ winter-’ or, as he preferred to 
call them, ‘ resting-eggs,’ was always associated with the appearance 
1 Although Prof. Whitman’s paper is entitled ‘‘Spermatophores as a means of 
hypodermic impregnation,” it does not appear that spermatophores are formed in 
Hydatina, the only rotifer in which the process has been observed with certainty. So 
far as we know, such structures have only been observed in Paraseison (Plate, 14) and 
in Asplanchna helvetica (Masius, 18). 
