324 WILLIAM A. HASWELL. 



This observation renders evident the purpose of the pair 

 of claspers with their adhesive glands and the peculiarly 

 shaped penis. In the act of copulation the male, holding the 

 female fast by means of the claspers, drives the sharp-pointed 

 penis through the body-wall in the neighbourhood of the 

 mature ovum, and discharges a spermatophore into the body- 

 cavity. 



Fertilisation is thus internal, but the fertilised ovum would 

 appear to be deposited at once, as no segmenting ova were 

 ever found. The section represented in fig. 12 shows definite 

 processes given off by the ovum towards the mass of sperms ; 

 these may be of the nature of receptive prominences, or 

 perhaps are processes formed during maturation. The body 

 lettered 'pl. in fig. 12 is most probably a polar body. 



As it passes out the oosperm becomes enclosed in a firm 

 shell, and is attached to the axis of a gill-plume or an epipo- 

 dite, usually near its base. 



Only a few stages in the development of the embryo have 

 been examined ; a full account of this part of the subject I hope 

 to be able to communicate at some future time when sufficient 

 material is available. So far as they go, my results are in 

 full conformity with the hypothesis dealt with in the following 

 section, that the Histriobdellidse are derived from the Roti- 

 fera. When it escapes from the egg, the young Histriodrilus 

 is fully formed in all respects, except as regards the repro- 

 ductive organs. 



Affinities of the Histriobdellidse. 



P. J. van Beneden (1) in his earliest communication on the 

 subject referred Histriobdella with doubt to the Poly- 

 chseta, as perhaps the larva of a Serpulid. In. his later 

 paper (2) he assigned it to the Hirudinea. 



Foettinger (6) enters into a full discussion of this question, 

 and comes to the conclusion that Histriobdella is nearly 

 related to Polygordius and Protodrilus, and ought to be 

 looked upon as a member of the class Archiannelida, and 



