CCELENTERATA: HYDROZOA. 



87 



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 devel- 

 ops itself into ■ a much more complicated structure. The 

 gonophore (fig. 13, <r) 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 " gonocalycine 

 canals." The gonophore, thus constituted, may remain per- 

 manently attached to the parent organism, as in Tubularia 

 indivisa (fig. 14, c); but in other cases still further changes 

 ensue. In the higher forms of development (fig. 14, rf) -the 



Fig. 14. — Reproductive processes of Hydrozoa. d Sporosac ; h Disguised medusoid ; 

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

 ing indicates the rejproductive organs, ovaria or spermaria. The part completely 

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



manubrium acquires a mouth at its free or distal extremity, 

 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 mar- 

 ginal tentacles and with an inward prolongation from its 

 margin, which partially closes the mouth of the bell, and is 

 termed the "veil" or "velum." By the contractions of the 

 gonocalyx, which now serves as a natatorial organ, the gono- 

 phore is propelled through the water. The manubrium, with 

 the shape, assumes the functions of a polypite, and its cavity 

 takes upon itself the office of a digestive sac. Growth is 



