1898] REPRODUCTION OF THE ROTIFER A 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. 1 

 M'Munich 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 Man pas, whose importaut 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 Eotifera, for cloacal coition has been seen by 

 many observers, and has been figured by Weber (15) in Diglena 

 cattlliim. 



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 

 Lacinidaria (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 

 ETydatina, 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 Asplancfma helvetica (Masius, 18). 



