82 MANUAL OF ZOOLOGY. 



polypary of the Corynida, when present, is readily distinguished 

 from that of the Sertularida, by the fact that in the former it 

 extends only to the base of the polypites ; whereas in the 

 latter it expands to form little cups for the reception of the 

 polypites, these cups being called " hydrothecae." 



As regards the reproductive process in the Corynida, the 

 reproductive elements are developed in distinct buds or sacs, 

 which are external processes of the body-wall, and have been 

 aptly termed " gonophores " by Professor Allman. Great 

 variations exist in the form and development of these gene- 

 rative buds, and an examination of these leads us to some of 

 the most singular phenomena in the entire animal kingdom. In 

 some species of Hydractinia and Coryne, the generative buds or' 

 " gonophores" exist in their simplest form; namely, as protuber- 

 ances of the endoderm and ectoderm, enclosing a diverticulum 

 of the somatic cavity. In this form they are attached to the 

 "trophosome" by a short stalk, and they are termed "sporo- 

 sacs" (fig. 14, a). They are exactly like the buds which we 

 have already seen to exist in the Hydra, with this difference, 

 that they are not themselves developed into fresh polypites, 

 but are simply receptacles in which the essential elements of 

 generation the ova and spermatozoa are prepared, by the 

 union of which the young Corynid is produced. 



In Cordylophora (fig. 13, H] a further advance in structure is 

 perceptible. The gonophore now consists of a closed sac, 

 from the roof of which depends a hollow process or peduncle 

 the "manubrium" which gives off a system of tubes which 

 run in the walls of the sac. For reasons which will be imme- 

 diately evident, the gonophore in this case is said to have a 

 "disguised" medusoid structure (fig. 14, b). 



In certain Corynida, however, we meet with a still higher 

 form of structure, the gonophores being now said to be 

 " medusoid." In these cases the generative bud is primitively 

 a simple sac such as the "sporosac" but ultimately deve- 

 lops itself into a much more complicated structure. The 

 gonophore (fig. 13, c) is now found to be composed of a bell- 

 shaped disc, termed the " gonocalyx," which is attached by its 

 base to the parent organism (the trophosome), and has its 

 cavity turned outwards. From the roof of the gonocalyx, 

 like the clapper of a bell, there depends a peduncle or 

 " manubrium," which contains a process of the somatic cavity. 

 The manubrium gives out at its fixed or proximal end four 

 prolongations of its cavity, in the form of radiating lateral 

 tubes, which run to the margin of the bell, where they com- 

 municate with one another by means of a single circular canal 



