The Latero-Sensovy Canals and Related Bones in Fishes. 423 



undoubtedly, in the latter cases, fused with the dorsal end of the 

 next anterior ossicle of the chain. This next anterior ossicle lodges 

 a sense org-an, in the adults of both Ameiurus nebulosus and Ameiurus 

 melas; and this organ must be the one that has, in larvae of the 

 former fish, the position already referred to as corresponding so 

 exactly to that of the postfrontal organ of Amia. Assuming it to be 

 that organ, the long bone that lodges it, and which occupies practi- 

 cally the entire postorbital portion of the infraorbital chain, must be 

 the homologue of the postfrontal of Amia. In Ameiurus melas the 

 organ in this long ossicle, Herrick's infraorbital organ No. 6, is said 

 by that author to be the onl}^ canal organ innervated by the outer 

 buccal of his descriptions. Certain of the remaining branches of the 

 outer buccal nerve are said by Herrick to definitely supply, and 

 certain others to apparently supply, what he designates as small pit 

 organs of the region. And what he regards as a detached filament 

 of this same outer buccal nerve is said to supply infraorbital organ 

 No. 5. This break in the innervation of these two outer buccal organs, 

 corresponding as it does with a break, between the two organs, in 

 the enclosing of the canal, would certainly be in favour of the 

 assumption that organ No. 6 is the postfrontal organ of the line. 

 Furthermore, the position of the bone thus identified as the post- 

 frontal, in Ameiurus, much resembles that of the postfrontal of many 

 reptiles, with which bone it is quite certainly homologous. 



The squamosal, in the several specimens of Ameiurus nebulosus 

 that were examined, lodged three sense organs of the main infra- 

 orbital line; one of them lying anterior to the point of anastomosis 

 of the preoperculo-mandibular canal with the main infraorbital, and 

 two of them posterior to that point, a primary tube leaving the canal 

 between the two latter organs. There was no separate extrascapular 

 bone in any of my specimens. Herrick says [47, p. 228] that he found 

 a separate extrascapular bone in one of the two specimens of A. nebu- 

 losus examined by him, but not in the other. In Ameiurus melas he 

 found a separate extrascapular, and it lodged the second organ found 

 in the main infraorbital canal posterior to the point of anastomosis 

 of that canal with the preopercular canal. It is thus practically 



