ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 895 



the Rhyncobdellidfe by tlie disappearance of all traces of a lateral 

 sinus and of the dilatations connected therewith, as well as by the loss 

 of all traces of the dorsal and ventral vessels ; the lateral vessels and 

 their connection with the dorsal and ventral sinus-system communi- 

 cate only by a newly developed botryoidal tissue, which may play an 

 important role, by forming a secondary coelom. The communication 

 between the existing coelom and the true vascular system occurs 

 either by vessels terminating with an open mouth, which is appa- 

 rently provided with a sphincter in certain portions of the ccelom 

 (c. g. the lateral dilatations and the branchije) ; or vessels may 

 acquire a connection with new spaces forming in the connective 

 tissue, which communicate on the other hand with small coilomic 

 remnants. The former method is characteristic of the Khynco-, tho 

 latter of the Guathobdellidas. 



After discussing in detail the characters of tho nephridia of 

 different genera, Mr. Bourne states his general conclusions with 

 regard to them; he finds that they "present a serial arrangement 

 with regard to their metameric repetition." The simplest condition 

 is seen in Clepsine, where the nephridium in all cases opens into 

 the ccelom on the one hand and to the exterior on the other. 



The author concludes with a discussion of the question whether 

 the Hirudinea are Platyhelminths, or more closely related to the 

 Chjetopoda. An answer to such a question must be based on a 

 knowledge of (1) the amount of variability in any particular system 

 of organs within the group itself, (2) the adult conditions of the 

 systems of organs in the group as compared with other groups, and 

 (3) the ontogenetic history of individual genera. 



The last is not here used ; as to the first, we note similarity of 

 structure in many points, but variability in the characters of the 

 anterior sucker, in the number of annuli forming a somite, and in 

 the amount of ccelom present. "The curious distribution in the 

 amoimt" of variability points to the very archaic nature of the 

 group ; the genera now living seem to have had an ancestor which 

 presented as high a development of each system of organs as is found 

 in any single genus of living Hirudinea. 



Mr. Bourne thinks that it is quite impossible to prove that the 

 Leeches are more highly developed Triclada or degenerate Cha^topods. 

 " The genetic relations are indirect and not direct." They present a 

 resemblance to the Platyhelminth (1) in the possession of median 

 genital pores; (2) in the suckers, to a certain extent; (3) in tho 

 general arrangement of muscles; and (4) in the structure of the 

 pharynx of the Khyncobdellida3. They differ from Chfetopods in 

 the absence of parapodia and seta), though the latter are, it is to be 

 noted, absent from Polygordius and Branchiohdella. They agree with 

 some Chajtopods in the presence of a clitellum and in the habit of 

 forming cocoons. The metamerism of the two groups may have been 

 awjuired separately and be due to different causes. 



No definite statement as to the affinities of the Leeches can be 

 given until wc know the developmental history of the ctclom in tliem 

 and in the Platyhelminths; the balance of evidence is certainly in 



