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THE AMERICAN NATURALIST. [Vol. XXXVII. 



cells in the distal end of the bud, a plug of ectodermal cells is 

 formed which grows down into the medusoid cavity, forcing back 

 the entoderm as it advances. This retreating fold of entoderm, 

 as it doubles upon itself by the increased growth of the ecto- 

 dermal plug, presses closely upon only four meridional areas of 

 the stationary layer of entoderm. By this process, four equi- 

 distant spaces or chymiferous channels are left in direct com- 

 munication with the medusoid cavity. These spaces constitute 

 the beginnings of the radial canals. (Fig. 9, c.) As these chan- 

 nels continue to elongate, they become dilated at their extremities 

 into bulb like ex- 

 $ nansions which 



mass of cells 



lying between the bell and the manubrium, and which are of 

 ectodermal origin, give rise to the future reproductive elements. 



9» g) Tne inner ectodermal layer of the bell, and the 

 ectodermal layer of the manubrium arise as successive differ- 

 entiations of the germinal layer. (Fig. 10, t. c.) 



L. Agassiz ('62, p. 278) says, "the medusa buds of this 

 Hydroid do not become free individuals, but remain attached, 

 develop their generative material and then wither and die." 



A. Agassiz ('65, p. 193) on the other hand, in speaking of 

 the Medusa of Corymorpha pendula says, "Although the separa- 

 tion of this Medusa from its Hydrarium has not been observed, 



