130 ME. F. J. COLE ON THE STEUCTUKE AND MOEPHOLOGY OF 



and nerve tracts. The sense organs were then systematically mapped out from the 

 sections, so that it is hoped any possible chance of error has been removed. 



Suxtra-orhitul Canal. — There are five sense organs on the supra-orbital canal as against 

 four dermal tubules. As a rule, one sense organ is placed midway between the internal 

 openings of two dermal tubules, so that there is usually a rough correspondence between 

 the number of sense organs and that of the tubules. The first sense organ on the supra- 

 orbital canal is placed between the openings of the first and second dermal tubules, but 

 nearer the second ; the second between the second and third tulmles, but nearer the 

 third (just over the anterior extremity of the nasal sac) ; the third and fourth anterior 

 and slightly posterior to the supra-orbital commissure respectively ; and the fifth near the 

 posterior extremity of the canal, and in the young forms * exactly dorsal to the optic 

 chiasma. 



Infra-oi'hital Canal. — This canal has eleven sense organs and ten dermal tubules. The 

 first two sense organs are situated between the first and second tubules, and just under 

 the first sense organ of the supra-orbital canal. There is a slight overlapping on the 

 part of the first two sense organs, the j^osterior extremity of the first being above the 

 anterior extremity of the second, and the two together extending practically from the 

 opening of the first dermal tubule to the second. The next six sense organs, the third to 

 the eighth, lie between their respective tubules as shown in the figure ; the ninth and 

 the tenth, however, are not separated by a tubule, and this seems to imply that the ninth 

 dermal tubule has degenerated. This tubule is indeed present in G. morrhua, and in 

 such a position as would separate the ninth and tenth sense organs of G. vwens. It is 

 therefore possible that in the latter species the tubule has existed and disappeared. The 

 eleventh sense organ lies between the ninth and tenth tubules, but somewhat nearer the 

 former. 



Hyomandihular Canal. — Twelve sense organs and thii'teen dermal tubviles were found 

 in connection with this canal. The first sense organ is slightly anterior to the opening 

 of the second tubule, and the second has the same relations with the succeeding tubule. 

 The remaining ten sense organs are situated between the openings of the tubules as 

 indicated in Plate 22 the last being placed on the narrow portion of the canal at its 

 posterior extremity. 



Lateral Canal, — The supra- temporal segment of the lateral canal has two sense organs 

 and two dermal tubules, the first sense organ being placed slightly posterior to the 

 opening of the first tubule, and the second lying between the ojjening of the second 

 tubule and the junction of the supra-temporal portion of the canal with the lateral 

 portion. The third sense-organ is found just anterior to the junction of the two canals 

 mentioned above, whilst the fourth is placed betweeu the third and fourth dermal 

 tubules. The remainder of the sense organs of the lateral canal are situated as usual 

 between the openings of the dermal tubules. The condition of the lateral canal in young 

 Cod behind the operculum will be described and discussed elsewhere. 



* See note on p. 150. 



