ZOOLOGY AND BOTANY, illCKOSCOPY, ETC. 603 



divergens, in whicli there is a large terminal vesicle in the median 

 dorsal line, which extends from the hinder extremity of the body to 

 near the ventral sucker ; into this sac two trunks open in a somewhat 

 jDeculiar manner, for they penetrate some way into it, preserving 

 their original diameter ; the number of ciliated infundibula is small. 

 The organs of Scolex trygonis pastinacece are next described. In 

 young forms of Tcenia echinococcus there is a complicated system 

 of fine canaliculi, which have their origin in the small ciliated infun- 

 dibula. 



The author then proceeds to some general considerations. He 

 now finds some important deviations from the primitive type to which 

 he first referred * this system of organs ; secondary foramina may be 

 developed and the terminal vesicle may disappear. To understand 

 these phenomena, we must first have a clear idea as to the con- 

 stitution of a Cestoid worm. The author is of opinion that we have 

 not to do with a true colony ; he looks iipon a proglottis as forming a 

 group of organs, and as comparable to the spermatophore-arm of 

 a Cephalopod. From the " point of view of individuality," the 

 Cestode is the equivalent of a Trematode, more altered in conse- 

 quence of its parasitic habit, considerably elongated, and more com- 

 plicated in consequence of the repetition of the sexual organs and 

 the tendency to metamerism. Primitively, the excretory apparatus 

 of an unsegmented Cestode communicated with the exterior, just 

 as does that of a Trematode, by a single posterior caudal fora- 

 men. But when the body became elongated, a moment appeared at 

 which the terminal vesicle was not sufiicient for its economy ; then 

 appeared the foramina secundaria. With greater development these 

 pores became symmetrically and regularly disti-ibuted over the body. 

 As they became more important, the duties of the terminal vesicle 

 diminished, and disuse led to atrophy. But though these organs 

 became " segmental," they do not seem to be the homologues of the 

 " segmental organs " of the higher Vermes. 



After a reference to the studies of preceding observers, and more 

 especially of Hatschek, whose essays have been fully analysed in 

 this Joui"nal, M. Fraipont asks whether we are justified in regarding 

 the segmental organs of a Cestode as the homologues of those of 

 an Oligochaste. He answers the question in the negative, for he 

 finds that the organ of the Cestode is differentiated from the head- 

 kidney, while in the Oligochfete it is probably a part of the longi- 

 tudinal canal ; so that in them it is an organ which has no homologue 

 either in the Eotifer or in the Flat-worm. He then deals with the 

 case of the Gephyrea, where the head-kidney persists for a time only, 

 and passes on to the trochophore-larva of the Mollusca. The author 

 concludes this part of his paper with the following words : — "£'«- 

 resume, we admit that the excretory apparatus of the Trematoda and 

 Cestoda is the homologue of that of the Ehabdocoela, Nemertinea, 

 and Eotifera, as well as of the head-kidney of the Annelida, Gephyrea, 

 and Mollusca. The Trochozoon-theory of Hatschek appears to us 



* See this Journal, iii. (1S80) p. 802. 



