242 CLAPP. [Vol. XV. 



Soon after the organ has reached the surface, there appears 

 on the summit a structure known as the " hyaline tube" or 

 "cupola." This was seen on specimens 2 cm. in length, being 

 easily observed with low magnifying power on the living fish, 

 some chloroform being added to the water to quiet the fish 

 durins; the observation. This tube measured .10 mm. in length 

 and .01 in breadth. From sections through the canal organs of 

 older fish, it is apparent that this "hyaline tube" is present 

 after the enclosure of the organs in canals. There is little 

 doubt in regard to the nature of this hyaline structure. The 

 cells of the organ, in common with other epidermal cells, may 

 secrete a cuticular substance on the free ends of the cells. In 

 the case of the hair cells this secretion is in the form of hairs 

 or bristles. These hairs may coalesce, forming a continuous 

 membrane, surrounding the central portion of the hillock, 

 thus forming the so-called tube, which is frequently present. 

 The hairs of the most central cells may remain separate within 

 this tube, as Leydig (i) observes in his most recent paper on 

 this subject. 



The "terminal buds" of Merkel or "end buds" of other 

 writers are not found on the surface of the head or trunk of 

 Batrachus, but they occur in the mouth and branchial cavities. 

 These organs are much smaller than the hillocks on the surface 

 of the body, and very little is known in regard to their 

 innervation. 



2. Lateral line nerves. — In his " Elasmobranch Fishes " Bal- 

 four {17) says that, in considering the subject of the lateral line 

 system, we are dealing with two distinct structures, (i) the 

 modified epidermis seen in certain lines along the sides on 

 the head and body, and (2) the accompanying nerves. 



The origin of the organs from the modified ectodermal cells 

 has been demonstrated, but the mode of origin of the accom- 

 panying nerves is not so well understood. Balfour {17), follow- 

 ing what he believed to be the analogy of cranial nerves in 

 general, held that the dorsal branches which supply the sense 

 organs grow out from the brain to these organs. On the other 

 hand, Gotte (21), Semper (22), van Wijhe (23), and Beard (16) 

 consider it certain that the cells from the ectoderm contribute 



