Wall of the Body-cavity of Vertebrates. 



237 



exists between the renal communications on the one hand 

 and the abdominal pores on the other. There are four 

 species with persistent nephrostomes and practically without 

 abdominal pores, and twenty-four species with abdominal 

 pores which lose the nephrostomes very early in develop- 

 ment. 



4. The Batoidei and the Carchariidae are characterised by the* 

 absence in the adult of open nephrostomes and the presence 

 of abdominal pores. 



In the above statements no account has been taken of the third 

 channel of communication present in all female Elasmobranchs, that 

 practicable through the oviduct after the disappearance of the 

 hymen. 



The relations thus brought to light afford a fairly complete account 

 of the distribution of both nephrostomes and abdominal pores 

 amongst adult Elasmobranchs. The total number of species (thirty- 

 six) from which these conclusions have been drawn is somewhat small 

 Avhen compared with the number of species on record in this group, 

 viz., more than 300. The families of the group are, however, all repre- 

 sented, with the exception of the Rhinodontidae, the Pristiophoridae, 

 and the Pristidae, in which nothing is known of the nephrostomes ; 

 but I found abdominal pores in a species from each of the Selachian 

 and Batoid families of Sawfishes. It follows then that with the two 

 species referred to and six additional species from various families 

 of Selachians known to possess abdominal pores,* there are forty-four 

 species in which the abdominal cavity is known to communicate with 

 the exterior, and not one in which this cavity is shut off from such 

 communication. So that we may extend the generalisations arrived 

 at from the discussion of the material here brought together to the 

 w r hole of the Elasmobranchii. It may hence be concluded that the 

 body cavity of adult Elasmobranchs is never completely enclosed by 

 the peritoneum ; it always communicates with the exterior, the com- 

 munication being effected in various ways, as shown above. 



The distribution of species with nephrostomes and of species with- 

 out them in the Elasmobranchii is clearly shown in Table I. The 

 scheme of classification adopted is from Dr. Giinther's ' Catalogue 

 of Fishes in the British Museum ' (published in 1870). 



A glance at Table I shows that the Carchariidae all close the 

 segmental tubes, three species of Scyliidoe retain them, four, prob- 

 ably five, species of Spinacidas do the same; also two species of 



* These eight species are : — Pristis zysron, Blkr., Pristiophorus cirratus, Lath., 

 HchinorMnus spinosus, G-m., Lamargus borealis, Scoresb., Chlamydoselachus angui- 

 neus, G-arm., Zygcena tudes, Cuv., Carcharias melanopterus, Q. and Or., and Car- 

 charias acutus, Buppel. 



