leatures of the sole. Tlie 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. 



Kow 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 apes of tlie snout. But on the left side anteriorly the 

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

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

 iilaments of the lower surface of the snout. 



In the cod [Gad us morr/ma) the lateral cephalic tube gives off another branch 



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

 the head of the sole, a, the anterior continuation of the lateral tube; t, the supra-tempoi-al tube; 

 c, the preopercular tube; (l\ the suh-ocular organs of the left side; I, the lateral Hue tube; 

 r.n., right nasal bone ; l.n., left nasal bom; ; t, the supi-a-temporal boue. 



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 platessa) 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 tlie 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 11 lie. 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 

 l)eliind the mouth- cleft below. 



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

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



