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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 



l.n. 



Fig. A. A diagram to illustrate the distribution of the epidermic sense-organs and dermal tubes on 

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

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

 r.?&., 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 platessd] 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 



