242 



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



Conclusions. 



The first inference to be drawn from the facts as here presented is 

 one bearing on the function of the abdominal pores. When some 

 conclusion has been reached as to whether the pores are mere 

 vestigial rudiments of no present physiological value, or whether 

 they are of real functional value to those vertebrates in which they 

 occur, then an attempt may be made to assign to them their morpho- 

 logical meaning. 



The opinion held by Bridge as the result of his investigations on 

 abdominal pores was, that, excepting in those cases where the genital 

 products passed out through them, they had no definite function. 

 It is now known that true abdominal pores do not serve as genital 

 ducts; the so-called abdominal pores of Cyclostomes, Muraenidae, 

 &c, are really genital ducts, and their homologies do not point to the 

 abdominal pores of the Elasmobranchs, &c. The pores would, accord- 

 ingly, be left without any particular function. 



This conclusion is, I believe, contradicted by the facts connected 

 with the relative distribution of nephrostomes on the one hand 

 and abdominal pores on the other. In the Elasmobranchs three 

 larger groups may be recognised. In one nephrostomes only occur, 

 in another abdominal pores only, in the third nephrostomes are 

 always present, while abdominal pores may or may not be added. 

 Amongst the Holocephala abdominal pores alone exist in the adult 

 Chimcera monstrosa. The Ganoids lose their nephrostomes, but 

 all have abdominal pores. All that is clear about the Dipnoi points 

 to the presence of abdominal pores in Ceratodus and in Protojpterus 

 annectens, nephrostomes being absent. The Teleostei with abdominal 

 pores have no nephrostomes. The Amphibia Csecilia and the 

 Amphibia Urodela both have nephrostomes opening a passage from 

 body-cavity to the exterior. In certain Chelonia and Crocodilia, 

 which close their nephrostomes during embryonic life, abdominal 

 pores are present. All the groups just mentioned have either 

 nephrostomes or abdominal pores, or in some (intermediate) cases 

 both together. In none are both openings absent, and it appears to 

 be necessary for some passage to be open between the body-cavity 

 and the exterior. This consideration gives, I believe, a clue to the 

 function of the abdominal pores. As they alternate on the whole in 

 their distribution with the nephrostomes, they undertake in all prob- 

 ability the duties of the absent nephrostomes, or when both are present 

 together they act in mutual support of each other. 



In what the function of the pores chiefly consists is demon- 

 strated by a very interesting experiment recently performed by 

 Guido Schneider.* He injected finely divided Indian ink mixed 

 * ' Anat. Anz.,' vol. 13, No. 15, p. 393. 



