116 EDWARD PHELPS ALLTS, JUN. 



groups. The tubules of the group radiate from the ampnlloe, 

 all running forward, forward and niesially, and backward 

 and laterally, in the general direction of tlie hind edge of the 

 mouth opening. The organs of the ampullae are all inner- 

 vated by a single short branch of the ramus mandibularis 

 externus facialis. 



The so-called pit organs, or sensory follicles, of other 

 descriptions of Mustelus I did not seriously attempt to fully 

 or carefully trace. Certain of them that are veiy evident 

 are shown in the drawings, and I doubt there being many 

 others. A very distinct line of them extends in a curved 

 line, as shown in fig. 3, across the entire ventral surface of 

 the head somewhat posterior to the mouth. At each lateral 

 end this line turns upward on to the lateral surface of the 

 head, passes posterior to all the ampullary pores of the region, 

 and posterior also to the hind end of the hyomandibular 

 lateral canal ; it then turns forward dorsal to and approxi- 

 mately parallel to the ampullary pores of the region, and 

 reaches the hind edge of the spiracle, where it ends. Its 

 innervation I could not determine, nor could I satisfy myself 

 as to whether the line was a line of sensory pit organs, or 

 simply a line of undeveloped ampulla) similar to those found 

 in my younger embryos. If the organs represent undeveloped 

 ampulla?, it would seem as if they, or at least a part of them, 

 must represent the hyoid group of ampullge of other fishes, 

 that group not otherwise being represented in Mustelus. If, 

 on the contrary, the organs are pit organs, of a lateral sen- 

 sory type, the ventral part of this line of organs recalls 

 markedly in its position the gular line of pit organs of Amia, 

 and may represent that line. In Ohlamydoselachus the 

 entire line would seem quite certainly represented in the 

 combined gular and spiracular lines of Clarman's (21) descrip- 

 tions, these lines being said by him to be open grooves. If 

 they are so represented it would seem almost certain that 

 the angular canal -of Ohlamydoselachus, which is clearly the 

 hyomandibular canal of Mustelus, must be the horizontal 

 cheek line of pit organs of Amia, and that the other lines on 



