THE GONOSOME. 



.33 



3. A coiitrndilc hell, in/ihrcUa (fig. 8, c), from tlie summit f)f wliosc concavity the maiiulirium is 

 suspended, and in whose walls is alvvaj'S developed a system of canals (^antrovancidar), consisting of 

 — 1. A set of c(|uiiiistant longitudinal canals (dd), mostly 

 four in numhcr, which radiate from the base of the 

 manubrinni, into which or into a special cavity {atrium, 

 fig. 17) which often exists at its base — they open at their 

 origin ; and 2, of a circular canal (e) which surrounds 

 the codonosloiiie, or orifice of the bell, and receives the 

 distal extremities of the radiating canals. 



4. Contractile tentacida {/), which spring from the 

 margin of the umbrella, and often carry at their bases 

 definite accumulations of pigment-granules (fig. S,y, and 

 fig. 17, c) named ocelli. 



5. A membranous extension, velum [It), of the margin 

 of the umbrella over the codonostome where it forms a 

 thin, muscular diaphragm, perforated in the centre by a 

 circular opening of greater or less diameter. 



The body composed of the various parts now 

 enumerated constitutes one form of the so-called " gym- 

 nophthalmic medusa,"^ and in its young state is usually 

 invested by an external protective membrane, the ecto- 

 theca, the homologue of the external layer of the peri- 

 goniutu in the sporosac. 



Of the form of medusa presented by the phanero- 

 codonic gonophore we have examples in the types 

 described by authors under the names of Sarsia, 

 Steenstrupia, Oceania, &c." 



4. The BladoityJe 



The blastostyle, as has been already said, must be 

 regarded as a hydranth whose alimentary functions have 

 become suppressed, and which, though not, properly speak- 

 ing, sexual itself, is entirely destined for the production of 

 sexual biuls or gonophores, either directly or through the 

 medium of a non-sexual bud, the blastochcme. A good 

 idea of this form of zooid may be obtained from the so- 

 called "fertile polypes" oi Hydractinia echinata (PI. XV, 

 and woodcut, fig. 4, (5 1}) . These are bodies of a cylindi-ical 

 shape, which are scattered among the alimentary hydranths, 

 and which in all respects they resemble except in the 



Oceania coronata, AUm. (provisiomUly),;i medusa 

 of unknown trophosouie, as an example of a plia- 

 nerocudouic gonophore. 



a, Manubrium ; i, generative elements (ova) 

 developed between endodenu and ectoJern of lua- 

 nnbriuni ; c, umbrella ; c', peculiar development 

 of the solid tissue of the umbrella, which occurs in 

 the present species ; dd, radiating gastrovascular 

 canals ; e, circular gastrovascidar canal ; f, mar- 

 ginal tentacles ; f, rudimental marginal tentacles ; 

 ^, ocellus ; i, mouth surrounded by its four fim- 

 briated lips. 



1 Another form is presented by the blastocheme described below. 



- The structure above described is that of the phancrocodonic gonophore in its most completely 



5 



