282 THE ELASMOBRANCH FISHES 



and has passing from it dorsally a sensory process. A sensory nerve leaves the 

 base of the organ and passes along with the lateral line nerve. 



Attention has been directed by several workers to the pit organs in sharks. 

 These have l)een studied recently for Squaliis acanthias by Norris and Hughes 

 (1920). Pit organs are here distributed between the lateral lines and anterior 

 to the first dorsal fin, and are supplied by the dorsal ramus (dr.X) of the 

 tenth nerve. In Heptanchus maculatus (fig. 229) this system of organs is 

 especially worthy of note since its organs have a segmental arrangement. In 

 places the lines of organs from one side to another are in almost unbroken 

 continuity, while other lines are limited to one side. 



