150 MK. F. J. COLE ON THE STRUCTURE AND MORPHOLOGY OF 



certain correspondence between the infra -orbital and byomandibular lateral canals, it 

 does not occur, as far as I am aware, in any other iish. And surely, in any case, the 

 corresjiondeuce has absolutely no significance. The byomandibular canal is situated on 

 a region morphologicaUi/ posterioi' to the infra-orbital canal, and cannot belong to the 

 same segments or segment of the head. If the correspondence had been l)etween the 

 supra- and infra-orbital canals (and these do not correspond either in Ainia, Gadus, or 

 any other fish that I know of), it might have had some significance, although, I am 

 inclined to think, very little. 



An interesting addition to the developmental litei-ature was made in 1891 by Wilson 

 {225), who was the first, I believe, to discover tliat the lateral line organs and auditory 

 organ may arise from a common sensory anlage. This seems to be oj)posed to the 

 metameric view, bnt Wilson himself believes it to be a physiological adaptation and to 

 have no phylogenetic significance. He favours Beard's views with regard to the head, 

 but does not think the lateral organs of the body were primitively segmental. 

 Cunningham (1890, 55) draws attention to the fact (p. 75) that in the Sole, " corresponding 

 to eacli scale of the lateral line, there is a pore in the skin which leads into the dermal 

 tube of the lateral line." On p. 81, however, he says : — " There is not a sense organ to 

 every scale of the lateral line ; in the middle of the body there is a sense organ on every 

 third scale : that is to say, there are two scales bearing no sense organs between two scales 

 which bear them. The position of the sense organ in relation to the scale on which it 

 is situated is always the same." Fig. 6, pi. xiv., shows this somewhat anomalous 

 condition. Without impugning the accuracy of Cunningham's statement, I may point 

 out that it is a remarkable exception to the almost universal law that there should 

 always be at least one sense organ between the openings of two dermal tubules *. 



Mitrophanow (1890, 141) confirms Wilson's statement re the common anlage of the 

 lateral line and auditory systems, and in 1892 (142) disagrees with Wilson and states his 

 belief that the lateral organs are not metameric. In a full paper published in 1893 (143) 

 Mitrophanow repeats his former statements, Imt adds that tlie common anlage gives rise 

 to the auditory organ, the lateral line organs, and Beard's branchial sense organs. He 

 considers this suflB.cient ground for maintaining that the lateral organs were not primi- 

 tively metameric, and says this conclusion is based on the study of all the Ichthyopsid 

 types he has investigated. Houssay (1891, 103), in an interesting review of Mitrophanow's 

 second work above, is inclined to accept Eisig's invertebrate origin of the lateral organs, 

 and combats Mitrophanow's statement that they are not metameric. 



Ayers (1892, 7) endeavours to show that the auditory organ is not supplied by a discrete 

 cranial nerve but by the branches of two cranial nerves, /. c. the facial and the 

 glossopharyngeal ( = tbe vagus: be considers the lateralis lateral line nerve to be a 

 branch of the IXth). He thus favours tlie metameric view of the lateral organs. On 

 p. 314 he says : — " As Froriep has shown, the ectodermal thickenings which Beard 

 described as giving rise to the lateral Hne organs have in fact another fate. The genuine 

 lateral line organs escaped Beai'd's observation, and in consequence Beard's conclusions 



* Sense organs may exir.t withoul dermal tubules (cp. Ewart & Mitchell, p. 10(»), but. mt viva verm. 



