OF POLYPES. 
47 
ation of the fleshy central part of the stem,) are enclosed in ve- 
sicles of the same texture as the polypidom itself, and neither 
proceed from, nor have any immediate connection with, the 
proper body of the polype, being evolutions from the pith or 
fleshy axis which connects the polypes together, and binds the 
various heads into one whole. — Such is a brief summary of the 
facts ascertained on this head, but it behoves me to mention 
that it is, to a certain extent, at variance with the opinions of 
Professor Grant. He maintains from his numerous observa- 
tions on a great variety of zoophytes, that the gem mules by 
which these animals propagate are highly organized portions of 
the gelatinous substance of the parent, formed 44 in almost every 
known zoophyte,” and not merely in the Hydrazoa, as we have 
limited it, 44 by the common connecting substance of the ani- 
mal, and not by the polypi, which appear to be only the mouths 
or organs of digestion. In Plumularise, Sertularise, Campanu- 
larise, horny Cellarise, Antennulariae, the ova are formed in ve- 
sicles which originate from the centre of the stem. In Flustrse, 
calcareous Cellarise, and some others, the ova are formed in the 
cells, but exterior to the bodies of the polypi , which disappear 
before the ova arrive at maturity. In the Lobularise, Gorgonise, 
Spongise, Clione, &c. the ova are formed and matured in the 
common fleshy substance of the body before they advance to be 
discharged through the polypi, or the fecal orifices.”* 
The gemmules exhibit considerable variety in colour, — they 
are milk-white, yellow, red, pink or green, but sometimes the 
colour is not fully developed until near maturity. In all the as- 
cidian polypes they are globular or have a tendency to that form, 
and appear to preserve it until after their discharge from the 
body ; but in the Hvdroida this is not the case, for although 
spherical in their earlier stages, 44 their shape alters on approach- 
ing maturity ; it elongates, becomes elliptical, next prismatic, 
and at length each corpusculum issues as a perfect animal from 
the orifice of the vesicle,” and exhibits in figure and in motion 
much resemblance to the little leech-like Planarise. (Fig. 6.f) 
* Edin. Journ. of Science, No. 14. 
f The figures represent the gemmules of Plumularia plurna. For the draw- 
ing I am indebted to my friend Dr Coldstream of Leith. 
