142 



THE ELASMOBRANCH FISHES 



ABDOMINAL POEES 



The abdominal pores in the Elasmobranchs may perforate the tips of the 

 papillae or, as was just said, they may pass through the cloaeal pits. Some of 

 the types having perforated papillae are Triakis semifasciatus, Carcharias 

 glaucus, Zygaena, Mustelus. In some the papillae are imperforate (Squatina) . 

 The slit-like type of abdominal pores is in connection, not with the papillae, 

 but with the cloaeal pits. This type is especially common among the rays. 



A B 



Fig. 141. Sections through rectal gland. (From Howes.) A. Zygaena. B. Baja. 



The abdominal pores vary so greatly in different species and in fact in 

 different individuals of the same species as to suggest that they are vestigial 

 structures. In the Cyclostome fishes they function as apertures through which 

 the sex cells leave the body; but in the Elasmobranchs, if the pores have ever 

 been thus used, this function has been lost upon the appropriation of special 

 channels formed for the passage of the sex cells. It hence becomes a question 

 whether or not in the Elasmobranchs the openings subserve any particular 

 function at the present time. 



