9 6 



MANUAL OF ZOOLOGY. 



and embryos are produced. These embryos, however, instead 

 of resembling the organism which immediately gave them birth, 

 develop themselves into the fixed Corynid from which the 

 gonophore was produced, thus completing the cycle. 



The swimming-bell of the medusiform gonophore is believed 

 to be formed by a great development of an inter-tentacular 

 web, such as is sometimes present, in a rudimentary form, in 

 the nutritive zooids. Sometimes the medusoid becomes quies- 

 cent towards the close of its existence, and the swimming-bell 

 becomes reversed or atrophied. Lastly, in Clavatella, the 

 sexual zooid, though free and locomotive, is not provided with 

 a swimming-bell, but creeps about by means of suctorial discs 

 developed on branches of the tentacles. 



As we have seen, the generative 

 buds of the Corynida may exist in the 

 following chief forms: i. As "spo- 

 rosacs," 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 ; but which never 

 become detached. 4. As perfect 

 medusiform gonophores (fig. 21), 

 which are detached, and lead an 

 independent existence for a time, 

 until the generative elements are 

 matured. In whichever of these 

 forms the gonophore may be pre- 

 sent, the place of its origin from the 



a Central poiypite or trophosome may vary in different 



manubrium; b Radiating gastro- r . r . J . * _,. 



vascular canals ;cCircular canal; SpCClCS Of the Order. I. 1 hey may 



m Marginal bodies ;* Tentacles. arise from the gides of the poly _ 



pites, as in C0ry* and Stauridia; 2. They may be produced from 

 the ccenosarc, as in Cordylophora ; 3. They may be produced 

 upon certain special processes, which are termed "gonoblastidia," 

 as in Hydractinia and Dicoryne. These gonoblastidia are 

 processes from the body-wall or coenosarc, which closely 



