Appendix to Cionistes reticularis. 
279 
the polypary ; in other species of Atractylis they arise from 
the reticulated base of the zoophyte. In certain species of 
the genera Sertularia and Campanularia, marsupial forms 
occur which bear no homological relation to each other. 
The gradual transition in the Hydroidse from the simple 
generative sac to the perfect Medusa is exceedingly interest- 
ing. I attempt to indicate it in the following sketch : — 
Generative elements (spermatozoa Or- 
oya) contained in a simple generative 
sac or dilatation of the ectoderm ; 'pla- 
centa formed of endodermal floor of 
sac, 
Placenta protruding into generative sac, 
and forming " spadix" (Allman) sur- 
rounded by generative elements, . 
— or branched and permeating them, 
— or folding round single ovum, 
Placenta adherent to summit of genera- 
tive sac ; summit of sac furnished 
with cluster of large thread- cells ; sac 
the equivalent of the peduncle of 
Coryne gravata, ... * 
Summit of sperm-sac furnished with a ') 
row of tentacles indicating the pre- ( 
sence of a non- differentiated subum- 1 
brella, ....,.) 
Generative sac transformed into a free\ 
walking medusoid ; peduncle furnished I 
with branched tentacles, as in Bou- \ 
gainvillea ; subumbrella not differen- ( 
tiated, its presence indicated by eye- j 
specks and otoliths ; umbrella absent, / 
Ovisac fixed, enclosed in a differentiated ] 
subumbrella with lateral and circular > 
canals and tentacles, . . . ) 
Hydra. 
Coryne. 
Hydr actinia. 
Campanularia 
lacaerta 
(male). 
Eudendrium 
rameum (fe- 
male). 
Eudendrium 
arhusculum 
(male). 
E. confertum 
(female).* 
Laomedea 
Loveni 
male). 
EleutJieria, 
medusoid of 
Clavatella 
(Hincks). 
^Simple gene- 
^ rative sac. 
Generative sac 
become a pe- 
duncle ("ma- 
nubrium," 
Allman). 
Subumbrella 
) present, but 
not differ- 
entiated. 
/ 
Laomedea ) Subumbrella 
Loveni (fe- > differen- 
male). ) tiated. 
* In the ovisac of E. confertum (see figure in margin), 
which I have had an opportunity of examining through 
the kindness of Mr Alder, the endoderm and ectoderm 
at first adhere together at the summit of the sac, and 
at this point a few large thread-cells occur in the ecto- 
derm. A similar occurrence of adhesion and thread-cells 
is found in the sperm-sac of E. arhusculum, and also in 
the false and mouthless peduncle of the medusoid of 
Coryne gravata. 
