THE HYDROPHORA. 



119 



termed nematophores by Mr. Busk. 1 In Ophiodes (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 (after Gegenbaur).— A, Hydranth : e, its peduncle ; «', hy- 

 drotheca ; o, mouth ; te, tentacles ; &', digestive cavity, continuous with the so- 

 matic cavity k, contained in the peduncle and in the creeping stem, 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 two, the budding gonophores project, 

 and may emerge from the summit of the gonangium i 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 2 has shown that, in Dicoryne conferta. the gono- 



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

 with the tentacles of Diphydce in my memoir on the "Affinities of the Medu- 

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



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

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



