IWTESTIKAT. CANAL OF THE ICHTHTOPSIDA. 405 



be indicative of homologieal relationship) ; the converse process 

 would tend towards that of the majority of the Teleostei and of 

 the higher Ichthyopsida*. 



If this comparison should stand the test of future investi- 

 gation, the folds of the intestinal mucous membrane in Gliiro- 

 centrus and the SalmonidcB will be non-homologous. To deny 

 that the large intestine of the majority of the Teleostei, as herein 

 defined, represents that of the higher Vertebrata, wouldbe, in tlie 

 present state of our knowledge, to imply that the comparative 

 method upon which our Eundameutal conceptions in morphology 

 are based is untrustworthy. 



The large intestine remains comparatiA^ely short through- 

 out the Ichthyopsida, the Sauropsida, and the lower Mam- 

 malia; it is not until au ascending term in the Mammalian 

 series is reached that it shows signs of clear differentiation into 

 the colon and rectum so well known among the higher repi'e- 

 seutatives of the same. That the caecum coli, however, not only 



* Owen and Hyrtl have long ago deseribecl in Protojpterus a median 

 diverticulum of the antero-dorsal wall of the cloaca, believed by them to 

 represent the virinary bladder. Parker has recently overthrown their inter- 

 pretation, and proposed (28. p. 14) to term the organ the ccscum cloaca — 

 coraparing it with the Plagiostome's appendix digitiformis ; his proposal receives 

 a specijil interest from the fact that Gilnthei' has described the appendix digiti 

 foi-mis of Chlamydoselache (11. p. 3) as " a globular glandular body of the size 

 of a large pea," which " lies dorsad of the cloaca, into which it discharges its 

 secretion by a short duct " — a condition unknown in any other Plagiostome. 

 Garman, on the other hand, speaks of it (10. p. 20) as " a CEecal pouch be- 

 hind the (spiral) valve." 



I am indebted to my friend Mr. G. A. Boulenger for the opportunity of 

 examining the parts in question in this Japanese Shark. Dr. Giinther does 

 not state exactly in what sense he uses the term "cloaca"' ; if by this we are 

 to under.=tand that portion of the gut situated posteriorly to the anal and 

 uriuo-genital orifices, Garman's description in perfectly correct. The duct 

 of the processus digitiformis is short and, like that of other Selaehii, forwardly 

 directed ; it opens but a short distance in front of the anus and much nearer 

 the same than in any other Plagiostome which I have examined. The whole 

 condition of the parts related favours the belief in the shortening up of the 

 large intestine arrived at above, and that is strengthened by the insignificant 

 size of the cloaca, which would appear to have been involved in the process. 



Parker's cfficum cloaca- opens directly backwards by a wide aperture ; it is 

 present in both sexes, and it might conceivably represent the conduit at least 

 of the Batoid processus digitiforujis {dv', fig. 1) in a much modified form. 

 It appears to me, however, to most nearly recall that diverticulum in the 

 female Ghimreroid which Hyrtl tei-med (Sitzb. Wien. Akad. Ed. xi. 1853, pp. 1085 

 -86) the " vesicula seminalis" and the absence of a corresponding vesicle in 



