58 



little (Fig. 2). This canal persists through a number of sections, and by 

 the time it has disappeared, three canals on the left are open, in the 

 positions formerly occupied by the three canals of the left side. One 

 is very minute, one larger, and one, in the lateral tract, is quite as 

 large as the central canal (which, however, is here small). (Fig. 3.) 



Fig. 3. C. S. Cord with three secondary canals present. 



All are lined with ciliated cells. These canals only persist for a few 

 sections and then a very short secondary canal appears on the right. 

 Two of the small canals on the left now reappear, and the canal on 

 the right grows larger, while the central canal is here very small, so 



that there are here present 

 in the cord four circular 

 openings, of about the same 

 size, and all lined with simi- 

 lar cells. 



About the same level 

 there occurs a remarkable 

 outgrowth from the dorsal 

 region of the cord (Fig. 4). 

 It is an outpushing from 

 the cord, with a narrow 

 neck, and includes one of 

 the secondary canals. This 

 outgrowth reaches the ex- 

 terior of the body, and lies 



Fig. 4. C. S. Cord with very small central canal, and two secondary canals, the 

 larger of these included in an outgrowth from the cord. 



