The Latterai Sensory System in the Mnraenidae. 149 



understand it. I. as already stated, interrupted my work on Conger 

 in order to investigate the canals in Mustelus, tlie results of which 

 I have recently published (No. 7). In text-figure No. 1 of that work 

 1 gave a hypothetical projection of the canals of Mustelus on to the 

 head of Amia. If that figure be consulted it will be seen, at once, 

 that the anterior portion of what I have there called the anterior 

 commissure of the infraorbital canal has almost exactly the position 

 of the ethmoidal canal of Conger. The ventro-posterior, or proximal 

 portion of the commissure in the projection of Mustelus is doubtless 

 represented in Conger by the line of surface sense organs that partly 

 encircle the base of the nasal tube of the latter fish. The resemblance 

 is much too striking not to warrant the assumption of an homology, 

 the other differences in the canals of the region being fully accounted 

 for by the presence of two nasal apertures in Conger instead of the 

 one in Mustelus. 



The ethmoidal canal of Conger is thus quite certainly the homologue 

 of a part of what Garman (No. 15) calls, in selachians, the nasal and 

 prenasal canals. The canal of Conger lodges two sense organs, and 

 should accordingly normally have three primary tubes and pores. The 

 anterior one of these three pores is the only one that has retained 

 its independence, and the short canal that leads from it into the 

 median sensory chamber is the anterior terminal primary tube of the 

 canal. The posterior pore has fused with the anterior pore of the 

 supraorbital canal to form a double pore. The intermediate or middle 

 pore of the line has quite certainly first fused with the corresponding 

 pore of the canal of the opposite side of the head to form a median 

 pore, and has then been secondarily closed in exactly the same way 

 that a corresponding pore has been secondarily closed in the same 

 region in both Amia and Polypterus (No. 5). In Polypterus, as in 

 Conger, a pore of the ethmoidal canal has fused with a supraorbital 

 poi-e. Init the arrangements in the two fishes are not strictly homo- 

 logous. It seems however almost unquestionable that the subrostral 

 portion of the infraorbital canal of selachians, the ethmoidal canal 

 and the line of surface sense organs that partly encircles the base of 

 the nasal tube of Conger, and the anterior, ethmoidal commissures of 



