MUSTELUS L.i;VIS. 127 



represented iii Mustelus by the uiandibular canal and the long 

 cheek line of surface organs. 



From the lateral lines of Chlamydoselachus, thus represented 

 in part by canals and in part by open grooves, Garmau derives 

 the canals of the Batoidei. 



We thus probably have, on the head of selachians, all the 

 lateral canal and pit lines of Amia excepting the middle and 

 posterior head lines of pit organs of my descriptions of the 

 latter fish, and no others. Both the supra-orbital and the 

 facialis part of the main infra-orbital canal lines of such 

 selachians as Mustelus come to a legitimate termination at 

 both ends by what seems to be an end anastomosis with 

 another canal. One should not, accordingly, expect to find 

 a line of unenclosed canal organs, such as certain of the pit 

 organs of Amia and teleosts certainly are, continuing the line 

 of the canal at either end. There should accordingly be, in 

 Mustelus, no pit organs on the top of the snout, and probably, 

 though not certainly, no anterior head line of pit organs. 

 The middle and posterior dorsal head lines of Amia then 

 alone remain to be accounted for of all the pit lines of. the 

 head of the latter fish, the mandibular, gular, and cheek 

 lines of Amia being probably all represented in Mustelus, in 

 the manner just above set forth. 



Is it, then, at all probable that the numerous am])ulhu of 

 Mustelus can possibly be represented in Amia by the few pit 

 lines on the head of that fish that are not almost definitely and 

 positively otherwise accounted for ? And is not the primary 

 distribution of the ampulho, as indicated by their pores, wholly 

 opposed to any such assumption ? The general distribution 

 of these pores, and their particular distribution in certain 

 places, closely resembles that of the terminal buds on the 

 head of larvae of Amia, and it is noteworthy that, in those 

 places in which certain of the pores of a single group of am- 

 pulla3 are arranged in line along each side of a lateral canal, 

 the branches of the nerves that innervate the organs of those 

 ampullae must straddle the lateral canal, and hence its related 

 nerve, exactly as the Irigtminal nerves that innervate the 



