(XELENTERATA : HYDROZOA. 73 



1 gonophores ' exist in their simplest form, namely as protu- 

 berances of the endoderm and ectoderm, enclosing a diverti- 

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

 to the ' trophosome ' by a short stalk, and they are termed 

 * sporosacs' (Jig. 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 Gordylophora (fig. 13 &) 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 



a 



Fig. 14. Reproductive processes of Hydrozoa. or. Sporosac. b. Disguised medu- 

 soid. c. Attached medusiform gonophore. d. Free medusiform gono- 

 phore. The cross shading indicates the reproductive organs, ovaria or 

 spermaria. The part completely black indicates the cavity of the inanu- 

 briiim and the gonocalycine canals. 



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 



