282 Proceedings of the Royal Physical Society, 
had been kept a few days in fresh water) I have figured with 
the camera in PI. XII. fig. 12. Its resemblance to Carus's 
figure of the Medusa, Cunina glohosa (Esch.), which I have 
copied in fig. 11, is very striking. 
As the Medusa is a multiplex organism, we must inquire 
how far it is homologous with the generative sac of the Hy- 
droid Zoophyte. 
Prof. Allman, in his paper on Cordylophora (Phil. Trans, 
vol. cxliii.), advanced the doctrine that the generative sac 
was homologous with the whole Medusa — a doctrine based 
upon an erroneous conception of the cavity in which the 
generative elements are contained. In a "Note on Dioecious 
Eeproduction in Zoophytes" (Edin. New Phil. Jour., vol. iv. 
p. 88), I stated that " the reproductive buds [generative 
sacs] (of Coryne) were filled with ova developed from the 
exterior of a hollow central stalk, a diverticulum of the 
alimentary canal;" and further, " The peduncle of the 
Medusa-bud [or budded Medusa] appears to me to be homo- 
logous with the entire reproductive capsule [generative sac] 
of Coryne glandulosa, &c" This view is now adopted by 
Prof. Allman, who writes, in Annals of Natural History,'* 
(vol. vi. ser. 3, p. 4), " The manubrium is the whole of the 
' peduncle,' ' stomach,' or by whatever other name it may be 
called, which depends from the centre of the umbrella in a 
Medusa or medusoid ; and I apply the same term to what 
I consider the homologous part in a sporosac, namely, the 
whole sporosac minus the ectotheca and mesotheca." Now, 
the 'sporosac,' less the ' ectotheca' and ' mesotheca,' is the 
simple generative sac, which, therefore. Prof. Allman has 
agreed with me in considering homologous with the peduncle. 
But I would now very much modify the above view. We 
must keep in mind that each of the eight elements of a 
medusoid has three distinct functional subelements ; that 
the single reproductive subelement of the Medusa exists, 
as in Stomohrachium, uncombined ; that where the peduncle 
is the reproductive organ of a free Medusa, as in Sarsia, it 
consists of two subelements of different function combined, 
each exercising its separate function, alimentative or repro- 
ductive ; that an organ composed of a single subelement (a 
