WITH NOTES ON THE WEST INDIAN SPECIES. 247 



debris, while others approximate to the character of roots, of which the first accurately 

 coincides with the anterior free border of the septum. This root is massive and solid 

 at its base and attenuated distally ; it occurs in the region of the buccal orifice of 

 the stomochord. The second root is slender, solid at its origin and sub-solid through- 



Fig. 1. Portion of transverse section through the middle of the collar of the specimen drawn on PI. XXVI. 

 Fig. 5D. The section shows the fourth root passing from the dorsal side of the medullary tube to the base- 

 ment membrane of the epidermis and illustrates the interpretation of the root and the septum in which it 

 lies, as a product of the raphe of fusion of the medullary folds. The superjacent epidermal groove pre- 

 sumably represents what is left of the medullary groove after the closing-in of its lower portion to form the 

 medullary tube (cf. PI. XXXII. Fig. 68). 



out, and does not fuse with the epidermis. The third root is similar except that it 

 meets the epidermis ; the fourth root does not fuse with the epidermis, neither does 

 the fifth and last, which is massive and presents disconnected traces of lumen. 



These observations may throw a partial light on the origin of the roots as 

 successive differentiations from the raphe of fusion of the medullary folds, but they 

 throw no direct light upon their character of hollow tubes passing from the medullary 

 canal to the epidermis. 



w. in. 35 



