Il6 MANUAL OF ZOOLOGY. 



In Cordylophora (fig. 41, 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 im- 

 mediately evident, the gonophore in this case is said to have 

 a "disguised" medusoid structure (fig. 41, l>). 



Fig. 41. Reproductive processes of Hydrozoa. a Sporosac ; b Disguised medusoid ; 

 c Attached medusiform gonophore ; d Free medusiform gonophore. The cross shad- 

 ing indicates the reproductive organs, ovaria or spermana. The part completely 

 black indicates the cavity of the manubrium and the gonocalycine canals. 



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. 41, 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 

 which surrounds the mouth of the bell. This system of tubes 

 constitutes what is known as the system of the "gastro-vascular" 

 or " gonocalycine canals." The gonophore, thus constituted, 

 may remain permanently attached to the parent organism, as 

 in Tubularia indivisa (fig. 41, c}\ but in other cases still fur- 

 ther changes ensue. In the higher forms of development (fig. 

 42) the manubrium acquires a mouth at its free or distal ex- 

 tremity, and the gonocalyx becomes detached from the parent. 

 The gonophore is now free, and behaves in every respect as an 

 independent being. The gonocalyx is provided with marginal 

 tentacles and with an inward prolongation from its margin, 



