THE HYDROPHORA. II9 



termed nematophores bj Mr. Busk/ In OpModes (Hincks) 

 they are tentaculiform. 



It frequently happens that the gonophores are developed 

 upon special stalks, each of which has essentially the struct- 



FiG. 15. — Campanularia (aner Gegcnbaur).— ^, Hydraiith : e, its peduncle; e', hy- 

 drotheca ; 0, mouth ; ^e. tentacles; A;', dii^estive cavity, continuous with the so- 

 matic cavity k, contained in the peduncle and in the creeping ^tem. S. B, gonan- 

 fium containing two medusiform zoSids or gonophores w ; the somatic cavity 

 '' is in connection with that of the creeping stem. C, Bud. 



ure of a mouthless hydranth. This is termed a blastostyle. 

 In some blastostyles (Fig. 15), during the development of the 

 buds of the gonophores, the ectoderm splits into two layers — 

 an inner, which invests the central axis formed by the endoderm 

 with the contained prolongation of the somatic cavity ; and 

 an outer, chiefly, if not wholly, chitinous layer. Into the in- 

 terspace between these tw^o, the budding gonophores project, 

 and may emerge from the summit of the gonaiigium^ thus 

 formed, either to develop the reproductive elements, and shed 

 them while still attached, or to be set at liberty as free medu- 

 soids (Fig. 16). 



Allman ^ has shown that, in Dicoryne conferta^ the gono- 



_ 1 They are described under the name of "clavate orgrans," and compared 

 with the tentacles o^ Diphydce In mv memoir on the "4ffinities of the Medu- 

 sae." ( "Philosophical Transactions," 1849.) 



2 'I Monograph of the Gymnoblastic, or Tubularian Hydroids," 1871, p. 31. 

 In. this beautifully illustrated and elaborate work, the student will find, not 



