DEVELOPMENT. 



79 



from what my observation of the process in Coryinorpha and other genera has led me to regard 

 as the true one. 



M'Crady^ believes that those medusae which occur among the gymnoblastic hydroids, where, 

 as we have already seen, they belong to the type of the gonocheme, arc developed in a different 

 way from those which " we find among the Campanularians, and where they present the type of 

 the blastocheme. He describes the umbrella in the former as produced by an excavation of 



Fig. 35. 



Segment of a young JEquorea captured off the west coast of Scotland, showing the developmeut 

 of the radiating canals. 



a. Mouth J 6, frill-like Hp ; c, floor of the greatly expanded base of the manubrium, from 

 whose circumference the radiating canals are emitted; rf, d, primary radiating canals; e, e, canals 

 developed later, and already united with the circular canal ; e', e', canals which have not yet reached 

 the circular cunal ; f,f,f,f,ca.m\\3 still less developed, on their way to the circular canal; 

 g,ff, developed marginal tentacles; h, h, h, rudiments of marginal tentacles; a, z, lithocyets ; 

 k, k, margin of velum. 



the substance of tlie young hud, forming thus a completely closed cavity in which the manubrium 

 is included, and which only at a subsequent period becomes perforated at its summit to form the 



Op. cit. p. 110. 



