Chap. II. 



THE DIFFERENT RADIATA. 



45 



Fig. 11. 



buds are not freed have no more the special structure of the Polyps descriljed 

 above, than those which jiroduce free Medusa?. 



Whether we consider their special structure or their genetic relation to certain 

 Medusa^, the Hydroids must be associated in close connection with the Medusce 

 proper; while their peculiar mode of reproduction, and 

 the greater simplicity of their structure when comjiared 

 to tliat of the covered-eyed Medusa^ show that they form 

 a distinct group in that class. This will be still more 

 evident, should I succeed in showing that all Hydroids 

 produce, in the same way, Medusa? buds ; even though 

 these Medusa; do not in all of them sepai'ate from the 

 mother stem to lead an independent life. The family 

 of Tubulario3 is most interesting in that respect, because, 

 while they all agree in their Hydroid state, there are 

 some, among them the genus Hjdjocodon {Fig. 11), for 

 instance, in which the buds {Fig. 11 d d, and Fig. 12), 

 though at first not diflfering from those of other kinds, 

 become free and lead an independent life as distinct, sexual, naked-eyed Medusa3 

 {Figs. 13, 14). In others, such as Tubularia proper, Thamuocnidia, and Parypha, the 



Fig. 12. Fig. 13. Fig. 14. 



HrBOCODON PROLIFEn, Ag. 



St*m of a single Hydra. — o Its moutk sur- 

 rounded with tentacles. — 1 1 Its marginal 

 tentacles. — ddd The most advanced of its 

 Medusas buds. 



Medusa bud of 

 Hybocodon trolifer, Ag. 

 t Base of attachment to the Hydra stock. 

 — o Proboscis. — c Circular chymife- 

 rous tube. — b Kadiating chymiferous 

 tube. — d t Proliferous Medusa with 

 its single tentacle. — t Single tentacle 

 of the primary Medusa. — Near c An- 

 other small proliferous Meduaa-bud, 

 and several others upon the main radi- 

 ating tube of the proliferous Medusa 

 d ?, between the letters d and t ; ex- 

 hibiting a striking analogy to Siphono- 

 phora^. 



Free Medusa of 

 Hybocodon prolifer, Ag. 

 Tlie largest vertical tube being 

 seen in profile. At first sight this 

 Medusa resembles much the Steeu- 

 strappia of Forbes ; yet it differs ge- 

 nerically. 



t' Proboscis. — r o Radiating tubes. — s 

 Circular tube. — t Tentacle. — m Buds 

 of Medusjc, proliferous from the base of 

 the single tentacle. 



Free Medusa of 

 Hybocodon prolifek, Ag. 

 Facing the largest chymiferons 

 tube, from the lower end of which 

 hangs tlie single tentacle, with many 

 small proliferous Medusas buds. 

 a Point of attachment before its separa- 

 tion from the Hydra stock. — be Radi- 

 ating or vertical chymiferous tubes, c 

 pointing to the circular tube. — t Ten- 

 tacle. — f Bunch of proliferous Medusae 

 buds. — e Rows of epithelial cells form- 

 ing distinct bands at the surface. — o 

 Proboscis. 



Medusa? buds produce new Hydroids without freeing themselves ; and yet these 

 Medusae buds sliow all the characteristic features of genuine naked-eyed Meduste. 

 In Tulndaria proper, for instance (Vol. 4, PI. XXIY. and XXVI., figs. 3 and 4), 

 they have four radiating tubes with a pendent proboscis and a circular tube, but 

 hardly a trace of tentacles; while in other genera these characters are variously 



