94 MANUAL OF ZOOLOGY. 



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. Strictly 

 speaking, Dr Allman understands by the term " gonophore " 

 only the ultimate generative zooid, that which immediately pro- 

 duces the generative elements.* Great variations exist in the 

 form and development of these generative buds, and an exami- 

 nation of these leads us to some of the most singular pheno- 

 mena in the entire animal kingdom. In some species of 

 Hydractinia and Coryne, the generative buds or " gonophores" 

 exist in their simplest form namely, as sacciform protuber- 

 ances of the endoclerm 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 " (rig. 20, 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 \vhich the essential elements of 

 generation the ova and spermatozoa are prepared, by the 

 union of which the young Corynid is produced. 



In Cordylophora (fig. 19, b) 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. 20, ^). 



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 develops 

 itself into a much more complicated structure. The gono- 

 phore (fig. 19, 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, 



* According to Mr Hincks, the "gonophore" is the bud in which the 

 reproductive elements are formed. "It consists of an external envelope 

 (ectotheca), enclosing either a fixed generative sac between the walls of 

 which the ova and spermatozoa are developed, or a free sexual zooid. " The 

 actual sexual zooid is termed by Mr Hincks the "gonozooid," whether it be 

 fixed or free in other words, it is the gonophore minus its external invest- 

 ment. The gonozooid is sometimes male, sometimes female ; and the same 

 colony may produce one or both the former being most commonly the 



