204 



TERATOLOGY AND PATHOLOGY. 



Fig. 77. 



a mouth and tentacles like those of the ordinary hydranths. Agassiz has described an occasional 



bifurcation of the spiral zooids of his Hydractinia 

 polyclina, and Hincks has figured a bifurcating 

 zooid of Hydractinia ecJiinafa in which one Ijranch 

 of the bifurcation carries tentacles and possesses all 

 the characters of an ordinary hydroid, while the 

 other is indistinguishable from a blastostyle though 

 no gonophores are developed from it. I have 

 myself seen the spiral zooids of Ilydractinina 

 ecJdnata depart from their normal condition by 

 developing tentacles on their distal extremities. 



Li Cordylopfiora lacudris an abnormal pheno- 

 menon, full of interest, may sometimes be seen. 

 This consists in the conversion of the spadi.x, after 

 the discharge of the generative products from the 

 gonophore, into a true hydranth (woodcut, fig. 77). 

 The spadix in this case, after it has performed its 

 function as a part of the gonosome, elongates itself 

 {b), differentiates an ectoderm, and developes upon 



A portion of a colony of Cordylopjmra ?a««<W«, showing J^g extremity a mouth and teutacles. 

 tbe transformation of a spadix into a hydranth. 

 o, A normal hydranth ; 4, the spadix of a gonophore 

 transformed into a hydranth after the discharge of the 

 generative elements from the gonophore ; c, the remains 

 of the external thin chitinous investment of the gono- 

 phore ; (Z, main branch. 



The conversion of the entire gonophore into a 

 hydi'anth in Mhizogeton firsiformis is described by 

 Agassiz,^ who regards it as a normal feature in the 

 hydroid. In this view, however, I cannot concur. 



I am quite of opinion that the phenomenon which Agassiz regards as normal is not so, and that 



it is one of the same class as that just described in Cordylophora. 



Cent. Nat. Hist. U.S.,' vol. iv, p. 12G, pi. xx, fig. 22. 



