MEM. M. C. Z., IX. No. 3. — ACALEFHS, POLYPS. 21 



the branch has been completed, and the portion thus separated has almost freed itself from the branch. 



7. A body of coenosarc (fiiistule) has dissolved its connection with the, hydroid, and become a free planula- 



like body swimming in the water. 

 24'. Hydroid formed by a gennnation from the free frustule. 

 24°. The frustule (7), after swinnning about in the water, secretes a mucus tube (S), into which it is represented 



in the figure as partially drawn on the right hand side (of figure). 

 24*. A bud has been sent out from the extremity of the frustule (ij 111). This bud increases in size, and ultimately 



forms the hydroid, with hydranth (24"). From the side of this hydroid a branch (77) is emitted. 



25"-25"'. Development of a Corbula in the family of Plumwlaridm. From Allman, op. cit., p. 60. 



25°^25''. AglaopJieiiia pluma. 



25". A very young corbula. I. rm. Lateral branch. 



25. Older stage of the corbula, with the ovarian vesicles (oa. vs.) already formed as spherical sacs, arising from 



the midrib of the corbula, between, the lateral rami {I. rm). 

 25°. The same, older, oa. vs. Ovarian vesicles, called gonangia. I. rm. Lateral rami (costai. ) hy th. Single 



hydrotheca. 

 25*. Mature corbula. The serrated bodies along the sides are called nematophores. The corbula is a specialized 



basket-shaped structure found in certain sei-tularian hydroids, for the protection of the vesicles and their ova. 



26. Young Ctjanea arclica, showing the umliral papillae. From Fewkes, Studies of the Jelly-fishes of Karragan- 



sett Bay. Bull. Miis. Com}). Zuol., Vol. VIIL, No. 8, PI. VH. fig. I. 



