92 EDWABD PHELPS ALLTS, J UN. 



formed or in process of formation^ and this lumen was always 

 most fully developed opposite the points from which the 

 cords representing tlie future tubules arose. In certain 

 places it extended outward a short distance in these latter 

 cords, but in no place did it reach the outer surface of the 

 head. On this outer surface of the head there was, however, 

 almost invariably, opposite the outer ends of the cords that 

 represent the primary tubes, a slight slit-like depression, the 

 appearance being that of a pre-existing opening that had 

 been closed by the pressing together of its walls. 



Even at this age, 55 mm., there was no perceptible 

 indication, in my sections, of the sensory organs in the main 

 canals, and the cords that represent the future tubules had 

 already begun to branch, and formed in certain regions a 

 somewhat complicated system. How these branching systems 

 arise could not be traced in my material, but it would seem 

 as if they must arise by the repeated dichotomous subdivision 

 of a single primary cord, exactly as the branching tubules of 

 Amia arise from a single primary tube (2). 



The ampullee in my 55 mm. embryo were nearly all repre- 

 sented by small teat-like processes that arose from the inner 

 surface of the ectoderm, and projected into the underlying 

 tissues. Some of these processes seemed solid, while others 

 contained a small central lumen which sometimes led to the 

 outer surface, the process then appearing as a sharp fold of 

 the entire ectoderm. A small nerve was easily traced to the 

 inner end of each process. While no attempt was made to 

 trace the complete and definite distribution of these little 

 processes, it was easily to be seen that in certain places they 

 had exactly the relations to the lateral canals that the 

 surface pores of the ampullary tubes have in the 12"2 cm. 

 embryo. This seemed to me to indicate that it must be the 

 pore in the adult, and not the ampulla, that indicates the 

 place of origin of the structure. Here, then, from the 

 primary distribution of these organs, as indicated by their 

 surface pores, was perhaps a manner of determining whether 

 they arose from pit-organs or from terminal buds. 



