THE CRANIAL NERVES AND LATERAL SENSE ORGANS OF FISHES. 183 



tbat it is the organ 16 of Allis that is wanting in Gadas, and further that dermal 

 tuhule 11 Amia corres])ouds to No. 8 Gadus. 



(4) Lateralis canal.— lleve it is at once obvious tliat the tirst organ of Amia 

 situated in the squamosal ( = the glossopharyngeal organ No. 17 infra-orhital Allis) is 

 absent in Gadus. The next four [Amia) are situated in the single supra-temporal or 

 extra-scapula, and these doubtless correspond respectively to the first four sense 

 organs and the four supra-teniporals of Gadus. It is possible that facts like this (and 

 there are many others) show that each sense organ had originally its own supporting 

 ossicle. The i^ost-temporal or supra-scapula of Amia has one sense organ, but none in 

 Gadus, whilst a further difference is that the scapula or supra-clavicle of Amia supports 

 a portion of the body canal and two sense organs, but takes no part in the support of 

 the canal system of Gadus. It is true that some authors consider the supra-clavicle a 

 post-temporal ossicle, but it is impossible to satisfactorily homologise the two bones, 

 and hence the difference between Amia and Gadus must remain. Behind the region 

 of the skull and shoulder girdle both forms agree in that the lateralis or body canal is 

 supported at intervals by small lateral line ossicles. 



We thus see that the two forms agree in a very remarkable nianner. This will be seen 

 if a comparison be made between Allis's tig. 49 and fig. 2 of this paper. Except that 

 Amia has more sense organs, and omitting differences in detail, the Ganoid form does not 

 differ as much from the Teleostean form as many of the latter do among themselves. 

 In fact the resemblances between the two are much more remarkable than their points 

 of difference. These facts of course strongly support the view originally maintained by 

 fossil Ichthyologists that the Ganoids cannot be ordinally separated from the Teleosts. 



Guitel (1890, 94) describes the lateralis lateral line nerve in Cyclopterids exactly as it 

 is in the Cod. There are the dorsal and ventral rami — the dorsal innervating the anterior 

 part of the body canal, and the ventral the posterior moiety. The same author (1891, 95) 

 has given us a somewhat full paper on the lateral line of Lophlus. He has unfortunately 

 made an insufficient study of the literature, and hence misnames the nerves. He states, 

 for example, that the supra-orbital caual is innervated l)y the " ophthalmique du trijumeau," 

 and also that a part of the operculo-mandibular line is supplied by " le nerf operculaire 

 superficiel du pneumogastrique qui echange des fibres avec I'operculaire superficiel du 

 facial." Further, the infra-orbital canal is said to be supplied by the " maxillaire superieur 

 du trijumeau." Guitel mentions Allis's first Amia paper, but omits to state on what 

 grounds he rejects the latter's nomenclature and adheres to the old views. His errors 

 are perhaps largely explained by the fact that he did not follow out the components of 

 the nerves with the microscope. A supra-orbital commissure is described as in Gadus. 



In Elasmobranchs we find the lateral line system in its most complex form. Beyond 

 in a very general way any comparison between the sensory canals of Elasmobranchs and 

 bony fishes is somewhat out of the question. This is very largely due to the absence of 

 dermal bones, which afford a very valuable guide in determining the homologies of 

 the individual sense organs and portions of the cinals. Ewart (1892, 68) describes 

 infra-orbital and supra-temporal anastomoses in Lcemaryus, the former lodging two 

 sense organs. The infra-orbital ;ilso anastomoses with the supra-orbital and hyo- 



