128 EDWARD PHELPS Al-LlS, JUN. 



terminal buds in Amiai, sti'addle certain of the lateral canals 

 and their associated, nerves (3). 



The ampulla) of Mustelus thus seem, in everything except- 

 ing- their special form and apparent innervation by the 

 facialis, to correspond much more closely to the terminal buds 

 of Amia than to the pit organs of that fish. As to this 

 apparent innervation of the ampullary organs by branches of 

 the lateral canal nerves, it is quite possible that the fibres 

 destined to the ampullary organs have a different central 

 origin from that of the lateral fibres, as I shall attempt to 

 show, after describing the nerves of Mustelus, by a com- 

 parison of the ophthalmic nerves of iishes. The fibres that 

 innervate the ampullary organs would, then represent a stage 

 intermediate between the terminal bud, or communis, fibres 

 of Amia, and the lateral canal ones. That such intermediate 

 stages should exist is wholly natural, if all the several forms 

 of special sensory cutaneous organs are derived from a 

 single primitive form, represented most closely by the 

 terminal buds of ganoids and teleosts, as Wiedersheim says 

 (64). 



In teleosts so-called pit organs, irregularly distributed 

 over the head, are frequently described. These organs, in 

 my opinion, must often be the homologues of the terminal 

 buds of Amia, and not of the pit organs of that fish. In this 

 I differ from Cole and Herrick, but Herrick, it is especially 

 to be noted, says (32, p. 37) that the pit organs of Menidia 

 are not situated in pits, being* '^ strictly naked papillee 

 projecting above the surface of the skin/^ He further says, 

 in the same work (p. 36), that he inclines to regard the 

 so-called accessory lateral line organs on the trunk of 

 Menidia, " like the buds on the top of the head, as belonging 

 to the communis system." 



Nervus Oculomotorius. 



The nervus oculomotorius of my 12'2 cm. Mustelus, as it 

 issues fx'om its foramen, lies directly mesial to the rectus 



