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leatures of the sole. The ventral opening of the supra-temporal bone leads into a 

 membranous separate tube, which passes beneath the skin in a ventral direction, runs 

 through a tube which pierces the preopercular bone, and is continued forwards to the 

 mandible. 



Now the supra-temporal tubes are, as we have seen, dermal, and pass through 

 apertures in a series of scales similar to those of other parts of the skin in structure. 

 On the right side the supra-temporal tube retains this structure throughout up to its 

 termination at the extreme apex of the snout. But on the left side anteriorly the 

 scales disappear, and the supra-temporal tube opens out on to the surface, its sense 

 organs becoming quite superficial : they are situated between the bases of .the tactile 

 filaments of the lower surface of the snout. 



In the cod [Gadus morrhua) the lateral cephalic tube gives off another branch 



F.'g. A. A diagram to illustrate the distribution of tlie epidermic sense-organs and dermal tubes on 

 the head of the sole, a, the anterior continuation of the lateral tube ; h, the supra-temporal tube ; 

 c, the preopercular tube; d', the sub-ocular organs of the left side; I, the lateral line tube; 

 r.n., right nasal bone ; l.n., left nasal bone ; t, the supra-temporal bone. 



besides those already mentioned, namely a sub-ocular tube, which is enclosed by a 

 series of scale-like bones, the sub-orbital bones. This sub-ocular branch is found in 

 the plaice [Pleuronectes jylatessa) on the right side as a canal in the derma beneath 

 the ventral eye ; while on the left side it exists as a dermal tube between the mouth 

 and the supra-temporal tube. In the sole I have been unable to find a trace of the 

 sub-ocular tube on the right side, but on the left side it is represented by superficial 

 epidermic sense- organs distributed all over the skin between the cleft of the mouth 

 and the sense-organs of the supra-temporal line. In the sole there are in addition a 

 number of superficial sense-organs along the line of the pre-opercular tube, forming a 

 single series along the upper part of that tube, and spreading out over the whole area 

 behind the mouth- cleft below. 



The lateral cephalic tube and the pre-opercular tube, which are to a large extent 

 enclosed in solid bone, nevertheless communicate at intervals with the exterior by 



