CCELENTERATA : CORYNIDA. 



closed in a chitinous investment, the name of " Gymnoblastic 

 Hydroids " is applied to them by Professor Allman. 



As regards the reproductive process in the Corynida, the 

 reproductive elements are developed in distinct buds or sacs, 

 which are external processes of the body-wall, and have been 

 aptly termed "gonophores" by Professor Allman. Strictly 

 speaking, Dr Allman understands by the term " gonophore " 

 only the ultimate generative zooid, that which immediately pro- 

 duces the generative elements.* Great variations exist in the 

 form and development of these generative buds, and an exami- 

 nation of these leads us to some of the most singular pheno- 

 mena in the entire animal kingdom. In some species of 

 Hydractinia and Coryne, the generative buds or " gonophores" 

 exist in their simplest form 

 namely, as sacciform protuber- 

 ances of the endoderm and ecto- 

 derm, enclosing a diverticulum 

 of the somatic cavity. In this 

 form they are attached to the 

 *' trophosome " by a short stalk, 

 and they are termed " sporo- 

 sacs " (fig. 40). They are exact- 

 ly like the buds which we have 

 already seen to exist in the Hy- 

 dra, with this difference, that 

 they are not themselves devel- 

 oped into fresh polypites, but are Fig. 4 o. Sporosac of ^rf 



cjmnlv rprpntarlps in whirh thp ata ( after Allman). a Outer wall of 

 mpij receptacles 111 wnicn tne the sac . b inner wall of the sac . s Col . 



essential elements Of generation umn developed from the floor of the 



the ova and spermatozoa are 

 prepared, by the union of which 

 the young Corynid is produced. 

 The sporosac is almost invariably 

 permanently attached to the trophosome, the only known ex- 

 ception being in Dicoryne, in which the sporosac, previous to the 

 discharge of its ova, liberates itself from its outer investment, 

 and swims about freely as an independent ciliated organism. 



* According to Mr Hincks, the "gonophore" is the bud in which the 

 reproductive elements are formed. " It consists of an external envelope 

 (ectotheca), enclosing either a fixed generative sac between the walls of 

 which the ova and spermatozoa are developed, or a free sexual zooid." 

 The actual sexual zooid is termed by Mr Hincks the "gonozooid," whether 

 it be fixed or free in other words, it is the gonophore minus its external 

 investment. The gonozooid is sometimes male, sometimes female ; and 

 the same colony may produce one or both the former being most com- 

 monly the case. 



sporosac, and extending into its cavity. 

 This is termed the "spadix;" it con- 

 tains a prolongation from the cceno- 

 sarcal canal, and the ova are developed 

 around it 



