MtJSTELUS L^VIS. 107 



pendicular to tlie ectoderm there were numerous short 

 tubules leading to the outer surface, and there opening by 

 pores. The whole group of tubules formed a large semi- 

 circular structure on the mesial edge of the canal. Both 

 anterior and posterior to it, along the entire length of the 

 canal, on both the dorsal and ventral surfaces of the head, 

 there were, excepting at the bend in front of the eye, no 

 tubules projecting mesially from the canal. All the other 

 tubules projected either laterally or directly outward toward 

 the external surface. This restriction of the tubules to the 

 lateral and dorsal aspects of the canal would seem, from 

 Garman's figures, to be a marked characteristic of the canals 

 of the head in the rays, though what its special significance 

 is is not evident. 



The 93 sensory organs found in the supra-orbital canal of 

 uiy embryo were all innervated by branches of the ramus 

 ophthalmicus superficialis, and were subdivided, by the 

 manner of their innervation, into six groups. The first 

 group includes organs 1 to IG, organ 16 lying approximately 

 in the plane of the anterior end of the nasal sac. The 

 second group includes organs 17 to 34, organ 34 lying imme- 

 diately posterior to the point where the canal anastomoses 

 with the anterior end of the infra-orbital canal. The third 

 group includes organs 35 to 58, organ 58 lying near the 

 point where the caiuil turns upward in front of the eye. 

 The fourth group includes organs 59 to 04, all of which lie 

 in the bend of the canal as it turns upward in front of the eye. 

 The organs of this group are related to those of the third 

 group more as a sub-group than as a separate and distinct 

 one. The next, or fifth group, includes organs (35 to 86, 

 organ 8Q lying in the plane of the foramen of the superficial 

 ophthalmic nerve. The sixth and last group includes organs 

 87 to 93, the organs of this group all lying posterior to the 

 superficial ophthalmic foramen, and being innervated by a 

 siugle nerve which leaves the ramus ophthalmicus super- 

 ficialis shortly after it leaves its foramen, and runs backwards 

 to the organs of the group. 



