The Latero-Sensory Canals and Related Bones in Fishes. 421 



The supraorbital canal shows, at this age, an anterior, nasal 

 l)ortion that contains two sense organs, and a posterior, frontal 

 portion that contain three organs. The course and position of the 

 canal shows that it will later anastomose with the main infraorbital 

 canal by its penultimate and not by its terminal primary tube, and 

 the canal is continued, posteriorly, by an anterior head line of pit 

 organs. 



The main infraorbital line has an anterior, ethmoidal portion that 

 is represented, on each side, by three surface sense organs, two lying 

 concentric with the inferior margin of the anterior nasal aperture, 

 and one on the top of the snout. These three organs retain, in the 

 adult, their embryonic surface position, not becoming enclosed in a 

 canal. And they do not apparently increase greatly in number, if at 

 all, in the adult, but my drawings are not definite in this particular. 



Other sketches that I have, show that the superior postorbital 

 organ becomes first enclosed in a section of canal that encloses also 

 the one otic organ of the horizontal part of the canal. Between these 

 two organs the canal bends sharply backward, and at the bend the 

 canal anastomoses with the penultimate primary tube of the supra- 

 orbital canal. The ossicle that forms in relation to the superior post- 

 orbital organ should therefore, by comparison with Amia and 

 Lepidosteus, be the dermal postfrontal of this fish; and the next 

 posterior organ should lie in the squamosal. 



There is, in older larvae, a surface line of pit organs that would 

 seem, from its position, to be the middle head line of those organs, 

 and Herrick [47] says that the innervation of a corresponding line in 

 Ameirus melas shows that it is that line. 



As in Ameiurus melas, and as also already stated by Herrick for 



A. nebulosus, there is no supratemporal commissure; but there are a 



number of scattered surface organs which I, at the time the drawings 



-were made, look to be the organs of the commissure. Herrick's work 



would seem to show this to be an error. 



In the adult Ameiurus nebulosus (fig. 7), the relations of the otic 

 and adjoining portions of the main infraorbital canal to the cranial 

 bones are perplexing, because the sphenotic, the postorbital ossification 



