The Lateral Line System in Siluroids. 549 



the transition to the condition of this canal in Chlamydoselachus. 

 Other homologies are to be discovered which however do not concern 

 us here. Has the branch no. 7 of Clarias, the representative pro- 

 bably of the groove in the coracoid plate of Coccosteus any homologue 

 in the animal kingdom? I have seen no record of any such unless 

 parts at least of the "pleurals" of Raiadae are such. 

 They pass out on the shouldergirdle. Garman appears to me to be 

 not quite clear in his attempts at explanation of their origin. In one 

 place he remarks: — "No doubt the pleural originated as a branch 

 of the orbital". Further on he says: — "The origin of the pleurals 



of the Batoids is a question of considerable interest. Our 



only clue to the solution of the problem is to be seen in Chlamydo- 

 selachus'". "The fact leads, at the least, to a strong pre- 

 sumption that the Batoidei are indebted for their pleurals and sub- 

 pleurals to a Galeoid ancestor resembling Chlamydoselachus as far as 

 the possession of spiracular and gular canals is concerned if not 

 further". 



In the absence of knowledge of the innervation one cannot speak 

 definitely but it appears to me more probable that the pleurals had 

 the same origin as the groove on the coracoid plate in Coccosteus 

 the rudimentary branches in the Siluroids. 



Conclusion. 



From the foregoing examination and comparison of the mucous 

 canals of certain Siluroids namely Clarias, Auchenaspis, Chaetostomus, 

 Trichomycterus and CalUchfhys, in addition to certain details the 

 following general results are arrived at: 



1) Clarias and Auchenaspis, two African Siluroids, resemble each 

 other in their lateral line system. 



2) Chaetosiomus agrees remarkably with the two preceding, some 

 structures rudimentary in the two first being fully developed in the 

 last. Chaetosiomus is a South American Siluroid. 



3) Comparison of the three preceding with Amia shows general 

 resemblances but no close genetic connection. The multifid systems 

 of pores in Amia are represented by simple pores in Siluroids, or 

 sometimes pores are absent. The pit lines of Amia are represented 

 by rudimentary canals in Siluroids. 



4) Trichomycterus and Callichthys, at young stages have similar 

 mucous canals which are little developed. 



