238 



Mr. E. J. Bles. On the Openings in the 



Notidanidae do so ; while all the JBatoidei lose the peritoneal nephri- 

 dial openings. Thus the classification here employed is in harmony 

 with the distribution of nephrostomes in adult Elasmobranchs. 



Table III. — In this table I have placed, side by side, the data 

 respecting the distribution of nephrostomes and of abdominal pores 

 in all the Vertebrates not yet dealt with, excluding the Cyclostomes. 

 The latter are omitted on account of the great probability that the 

 so-called abdominal pores of Cyclostomes are genital ducts, morpho- 

 logically as well as functionally, and hence quite distinct from true 

 abdominal pores, which are never used as genital ducts. 



The fishes in which the ova when mature fall into the general body 

 cavity usually have abdominal pores ; this applies to certain Elas- 

 mobranchs, the Holocephala, mos't Ganoids, some Dipnoi and to some 

 Salmonidae. But there are exceptions, as we have seen, amongst the 

 Elasmobranchs ; some Salmonidae have no pores, and other Teleos- 

 • teans with the primitive form of ovary have none, e.g., Mursenidae, 

 Galaxidae, &c. Then, on the other hand, there are fishes with tubu- 

 lar closed ovaries forming a continuous tube with the oviducts and 

 with a lumen quite distinct from the body-cavity, as it is in the 

 majority of Teleosteans, yet the body-cavity is, nevertheless, open to 

 the exterior through abdominal pores. Lepidosteus osseus is in this 

 condition, and, amongst Teleosteans, the Mormyridae. It follows 

 that there is no correlation between the condition of the ovary and 

 the occurrence of abdominal pores. 



It is noteworthy that in the Amphibia alone, amongst the Verte- 

 brates ranking higher than Elasmobranchs, do the nephrostomes 

 persist in the adult, and that the abdominal pores are entirely absent. 

 This is the more striking, since the abdominal pores reappear in 

 Reptiles, in the absence of nephrostomes. 



Equally important, from the present point of view, is the change 

 of function of the nephrostomes within the group Amphibia. In the 

 Gymnophiona and Urodela the original excretory function is served ; 

 but in Anura, where the lymphatic system is more highly developed, 

 the body-cavity has become a lymph space, and the nephrostomes 

 lead from it directly into the renal veins, not into the kidney tubules 

 (Nussbaum). The abdominal cavity of Anura is also, through the 

 stomata, in close communication with the lymphatic system, and so, 

 through the lymph-hearts, with the veins. Hence the body-cavity of 

 the lower Amphibia may be compared, as regards its relations to the 

 kidneys, with the body-cavity of certain Elasmobranchs (Cestracion), 

 while the relations of body-cavity and vascular system in the Anura 

 are parallel to those obtaining in the higher Reptilia and in Mammals. 



