MUSTELUS L.EVIS. 93 



To confirm my conclusion that the surface ampullary pore 

 represents, approximately, the place of origin of the am- 

 pullary organ, I sought in my younger embryos for the lines 

 of organs that should represent certain regular, constant, 

 and well-marked lines of ampullary pores in my larger 

 embryos. It will be sufficient to describe a single one of them. 



In my 12'2 cm. embryo there is on each side of the dorsal 

 surface of the head, and slightly anterior to the external 

 opening of the endolymphatic duct, a regular curved line of 

 ampullary pores. The tubes leading from these pores run 

 forward to a sub-group of the superficial ophthalmic group of 

 ampullae, these ampullee lying on the dorsal surface of the 

 nasal capsule. In the 55 mm. embryo there was, in exactly 

 the place occupied by these pores in the older embryo, a line 

 of surface sense organs which greatly resemble, in certain 

 respects, the pit-organs in larvae of Amia, while in others 

 they greatly differ from those organs. My material was not 

 adapted to a histological study of tbem, but it may be said 

 that the organs were represented by a series of processes 

 arising from the inner surface of the ectoderm, each process 

 enclosing a little space which may or may not be in direct 

 communication with the exterior. The processes all turn 

 anteriorly, parallel to the overlying ectoderm, and a small 

 nerve enters each process at its deeper or anterior end. 

 These short processes of this 55 mm. embryo thus unques- 

 tionably represent the complete ampuUse of the 12*2 cm. one. 

 The long ampullary tube that is found in the latter embryo 

 must then be formed by an exceedingly rapid growth of the 

 short process of the younger one, that process being, so to 

 speak, stretched out into a long tube between the fixed point 

 represented by its surface opening and another relatively 

 fixed one, represented by the point where the sensory nerve 

 enters the process. The tube apparently offers less resistance 

 to this stretching process than the nerve does. 



Further evidence that the ampullary pore does not usually 

 travel far away from its place of origin is found in the fact 

 that certain lines of these pores are frequently found on the 



