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. lb.—CampanuIaria (after Gegenbaur).— A, Hydranth : e, its peduncle ; «', hy- 

 drotheca ; o, niouih ; te, tentacles; k', digestive cavity, continuous with the so- 

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

 fium containing two medusiform zooids 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, chieflv, if not wholly, chitinous layer. Into the in- 

 terspace between these two, the budding gonophores project, 

 and may emerge from the summit of the go?iangium, 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 Dip hy dee in my memoir on the "Affinities of the Medu- 

 sae." ( "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 



