YOUNG STAGES OF LYMNOCODIUM AND GERYONIA, 201 
Relation to the morphology of Ctenophora and of Medusoid 
Gonophors.—I have already alluded to the reciprocal illustra- 
tion afforded by the development of the sub-umbral cavity 
in such gonophors as those of Hydractinia, and in meduse 
developing directly from the egg. 
The exceedingly important and (as I think) convincing 
reference of the Ctenophora to the Hydromedusa type, made 
by Haeckel (‘ Sitzungsber. der Jenaichen Gesells.,’ 1879, 
p- 70), is in no small degree rendered acceptable by the 
existence of directly-developing Meduse in which the sub- 
umbral space has the form of a closed chamber, or of a 
sac with but a narrow opening to the exterior. This 
sub-umbral sac appears to correspond with the so-called 
stomach of the Ctenophora, and its opening with the so- 
called mouth of those forms. In both cases it is lined by 
ectoderm, and develops quite independently of the endoder- 
mal cells, which give rise to the stomach and canals of the 
Hydromedusze on the one hand, and to the infundibulum 
and canals of the Ctenophora on the other hand. 
Balfour (‘ Embryology,’ vol. i, p. 145) compares the ecto- 
dermally-originating ‘‘ stomach ” of Ctenophora to a stomo- 
dzeum,' and more especially to the stomodeeum of Acraspedote 
Meduse (Scyphomeduse) and Anthozoa. 
But if this assimilation be well founded, the stomodeum 
of Scyphomedusze and of Anthozoa will be morphological 
equivalents of the sub-umbral space (sub-umbrellar cavity) 
of Hydromeduse ; and the question presents itself as to 
whether the stomodeum of the higher groups—with its 
wide dimensions and contractile walls—may not be similarly 
identified. Against such a view there appears to be a 
strong argument in the very general presence in higher 
animals of a “ proctodzeum ”—an anal ectodermal invagina- 
tion, parallel in its origin to that connected with the mouth. 
It may, however, be worth while to examine the facts of 
morphology in reference to this suggestion. 
1 The name applied by me and adopted by Balfour for the ectodermal 
invagination which gives origin to the mouth and first portion of the ali- 
mentary tract in all Metazoa except some Ceelentera. See this Journal, 
October, 1876. 
VOL, XXI,—NEW SER. ) 
