FREE-SWIMMING SPOROSACS OF THE HYDROID GENUS DICORYNE. 269 



the Neapolitan sporosacs the spadix lies to one side of the enlarged oocyte, in 

 D. conferta the spadix is situated between the two oocytes and, notwithstanding 

 considerable compression in the later stages, retains its original axial position through- 

 out development. Goette's observations on the development of the female sporosac 

 cease at a stage long before the appearance of the tentacles, but Allman has given 

 a moderately full description of the free, tentacled sporosac (1861, 1872). 



From direct observation we can add nothing to Allman's account, but the close- 

 ness of the developmental and structural relations between the male sporosacs of 

 D. conferta and D. conybearei, together with the similarity in the general lines 

 of development of the earlier stages of the female sporosac in these species, 

 suggest that the adult female gonophores of the two species will present similar 

 structure. We may, therefore, indicate probable additions to and slight emendations 

 in the description given by Allman. Some of the remarks made on his description 

 of the male gonophore (p. 268) apply also to the female, e.g. in regard to the 

 "ectotheca" and "endotheca" and their supposed homology with the layers of a 

 medusoid gonophore. Allman does not mention the formation of a constriction at 

 which the sporosac breaks away from the sporosac stalk, although such a neck is no 

 doubt formed in the female as in the male. Further, he states that " each ovum is 

 invested by a proper membrane, which presents the remarkable and unique character 

 of possessing considerable thickness and being richly set with thread-cell-like bodies " 

 (1872, p. 227). In connection with this statement we draw attention to the fact 

 that the oocyte of D. conybearei exhibits a differentiated peripheral zone of cyto- 

 plasm and not infrequently also a thin vitelline membrane, but these are not 

 cellular layers and they do not contain nematocysts. Probably the condition is 

 similar in D. conferta. 



Affinities of the Free-swimming Sporosacs of Dicoryne conybearei. 



The free-swimming sporosacs from Naples are evidently closely related to those 

 of Dicoryne conferta, and the former should undoubtedly be referred to the genus 

 Dicoryne. The origin and development of the gonads and of their investment 

 agree in the two cases almost to the smallest details, the main point of difference 

 being that the Neapolitan sporosacs possess only one tentacle and the female bears 

 one oocyte, while the sporosacs of D. conferta have two tentacles and the female 

 contains as a rule a pair of oocytes. 



A close relationship also exists between the sporosacs from Naples and those of 

 Heterocordyle conybearei, Allman, described by Allman (1872, pp. 307, 308 ; pi. x, 

 figs. 4-7) from material collected in Glengariff Harbour, Co. Cork, and by Weismann 

 (1883, p. 84, Taf. xi, figs. 7, 8) from Neapolitan specimens. Allman names the parts 

 of the sporosac of H. conybearei in accordance with his view of their medusoid 

 homologies, but from Weismann's account it appears that in every respect the 



