The Latero-Sensory Canals and Related Bones in Fishes. 451 



sac may be, as I was formerlj" led to conclude, the homologue of the 

 posterior process of the premaxillary of Amia, and hence, also, of the 

 deeper, membranous portion of the so-called ethmo-nasal bone of 

 Lepidosteus, this bone in each of these three fishes then perKaps being 

 a latero-sensory ossicle developed in relation to the olfactory organ. 

 For, notwithstanding the very positive neurological opinion that the 

 nose is not a latero-sensory organ, it certainly may be such an organ, 

 or a strictly homologous one, if Brauer [18] is correct in his conclusion 

 that the olfactory organ, the ganglion ophthalmicum, and the auditory 

 organ are all three homodynamous. 



Esox. Fig. 6 gives a lateral view of an embryo of Esox ameri- 

 canus, 22 mm long. The drawing for this figure was made in 1887—88, 

 and it is reproduced here simply to show that, in this fish, the supra- 

 orbital canal will quite undoubtedly anastomose with the main infra- 

 orbital hj its terminal tube; that the middle head line of pit organs 

 is very strongly developed, even at this age, consisting, as it does, 

 of seven relatively large sense organs on each side; and that the 

 supratemporal canal is represented by a single large sense organ only. 

 It also shows a curved line of smaller organs, on each side, in the 

 ethmoidal region, these organs undoubtedly representing the ethmoid 

 commissure; and a line of similar organs approximately parallel to 

 the dorsal edge of the mouth. This latter line I [3, p. 441] have 

 already shown to be quite undoubtedly the homologue of the horizon- 

 tal cheek line of pit organs of Amia. Still another line of still smaller 

 surface organs is seen immediately posterior to the nasal pit. This 

 line has no apparent homologue in Amia, but I found a similar line 

 in Conger, in which fish it is innervated by a branch of the superior 

 ophthalmic nerve. The position of this line of organs agrees fairly 

 well with that of the surface openings of the 2nd. group of ophthalmic 

 ampullae of my descriptions of Mustelus [8], but whether there is here 

 a possible homology, or not, I would not venture to say. 



Sketches that I have of older embryos of Esox americanus show 

 that the dorsal postorbital, or postfrontal organ is first enclosed in an 

 anterior prolongation of the squamosal canal, independently of the 



anterior part of the infraorbital line, and that, as in Amia and the 



29* 



