88 



MANUAL OF ZOOLOGY. 



rapid, and the gonophore may attain a comparatively gigantic 

 size, being now absolutely identical with one of those organ- 

 isms which are commonly called "jelly-fishes," and are tech- 

 nically known as Medusce (fig. 15). In fact, as we shall after- 

 wards see, most if not all of the gymnophth(ilmate Medusa, 

 originally described as a distinct order of free-swimming Hy- 

 drozoa, are in truth merely the liberated generative buds, or 

 ' medusiform gonophores," of the permanently-rooted Hydroids. 

 Finally, the essential generative elements — the ova and sper- 

 matozoa — are developed in the walls of, the manubrial sac, 

 between its endoderm and ectoderm, and embryos are pro- 

 duced. These embryos, however, instead of resembling the 

 organism which immediately gave them birth, develop them- 

 selves into the fixed Corynid from which the gonophore was 

 produced, thus completing the cycle. 



As we have seen, the generative 

 buds of the Corynida may exist in 

 the following forms : — i. As "sporo- 

 sacs," or simple closed sacs, con- 

 sisting of ectoderm and endoderm, 

 with a central cavity in which 

 ova and spermatozoa are produced. 

 2. As "disguised .medusoids," in 

 which there is a central manubrial 

 process and a rudimentary system 

 of gonocalycine canals; but the 

 gonocalyx remains closed. 3. As 

 complete medusoids, which have a 

 central manubrium, a complete sys- 

 tem of gonocalycine canals, and an 

 open gonocalyx j but which never 

 become detached. 4. As perfect 

 medusiform gonophores (fig. 15), 

 which are detached, and lead an 

 independent existence for a time, 

 until the generative elements are 

 matured. In whichever of these 

 ■ Free medusiform gono- forms the goiiophore may be pre- 

 fet %nS'pSypi'tf or s^ut the place of its origin from the 

 manubrium ; i* Radiating gasiro- trophosome may vary in different 

 rMtgiSiboiies?rTlL?a^ii: specics of the Order, i. They may 

 arise from the sides of the polypites, 

 as in Coryne and Stauridia; 2. They may be produced from the 

 coenosarc, as in Cordylophora ; 3. They may be produced upon 

 certain special processes, which are termed " gonoblastidia^" 



Fig. 15. 



