Appendix to Hydractinia. 
283 
generative one) having only one function, cannot be homo- 
logous with one composed of two subelements (peduncle of 
Sarsia), each having its distinct function, or with an organ 
of sixteen subelements (peduncle of Bougainvilled)^ eight 
of which are alimentary and eight reproductive. I would 
therefore now state — 
That the simple generative sac of Goryne is homologous 
with the reproductive subelement or single generative sac 
as it exists on the lateral canal of Stomohrachium. 
That the peduncle-like sac of Eudendrium confertum is 
homologous with the reproductive subelement in the pe- 
duncle of Sarsia — not with the whole peduncle. 
That where the generative sac evidently consists of many 
subelements, as in Tubularia larynx and Sertularia fallax 
(evidenced by the four summit-lips or lobes, the symmetri- 
cal character of each of which indicates it to be composed of 
two subelements), it is homologous with the reproductive 
subelements in the octopartite peduncle of BougainviUea, 
or, rather, with the eight coalescing reproductive subele- 
ments of Eleutlieria. 
I consider that a four-lobed or branched state of the pla- 
centa or spadix indicates a multipartite constitution of the 
generative sac, and not a rudimentary medusoid form of that 
organ ; for we have, in the fixed female medusoid of Lao- 
medea Loveni, a four-lobed condition of the placenta in the 
peduncle-like ovisac, with the existence of a well-differen- 
tiated subumbrella and lateral and circular canals. 
My space will not allow me to illustrate the homological 
relations which exist between the polypary (or coenosarc) 
and the polypidom on the one hand, and the subumbrella 
and umbrella on the other. This must be reserved for a 
future occasion, when I hope to fill up the gaps in this 
rough and incomplete sketch of some of the morphological 
relations of the Hydroidse and their Medusee. 
Appendix to Hydractinia, printed at vol. i. p. 192. 
In the " Annals of Natural History " (vol. iv. ser. 3. p. 50) 
Prof. Ailman has remarked, with regard to Hydractinia, 
that " the solid chitinous polypary [polypidom] is covered 
VOL. ir. 2 o 
