THE RADIATE INDIVIDUAL 



109 



is a repetition of reproductive organs, and in the neigh- 

 bourhood of the radial canals ; also one centrally placed 

 alimentary tract, and a nerve-ring underlying the water- 

 vascular ring. 



On the other hand, in the Starfish we find a true, or 

 closed ccelom contrasting with the " open " ccelom of the 

 Medusa (see page 98 ) ; and the Starfish's radial canals 

 do not connect with the digestive tract. In addition, the 



Fig. 39. — Illustrating suggested evolution of Eohinoderms. 

 1. Medusoid plan, with " open coelom " at v, the edge of the 

 velum encircling the mouth end of the manubrium. 2. The 

 same plan drawn with an anus opened at a, the radial canals, 

 re, being thus cut off from the stomach. The circular canal is 

 drawn smaller, and the velum as encroaching on the region of 

 the gullet. 3. The ccelom is drawn as completely closed by 

 an encroaching velum, and the circular canal and nerve-cord 

 encircle the gullet. By furnishing the radial canals with tube- 

 feet the plan is made the rough one of a sea-urchin, m, mouth ; 

 co, ccelom ; ce, circular canal ; no, nerve-cord ; tf, tube-feet. 



alimentary tract is sectioned off into special parts with 

 special functions, and, most important of all, ends in an 

 excretory orifice, or anus. Fig. 39 shows roughly the points 

 of resemblance and difference mentioned. 



On a previous page the suggestion was made that the 

 space between the bell and manubrium of a medusa is, so to 

 speak, the forerunner of the true ccelom of higher types ; 



