246 Natural History of British Zoophytes. 
lype quickly and almost coetaneously developes itself ; and this ori- 
ginal cell and polypus is as large, as perfect,, as fit for every pur- 
pose to which it is destined as any of those which are in rapid suc- 
cession evolved from its sides and apex, for age adds only to the 
number of individuals in the polypidom, and nothing to their per- 
fection. 
ADDITIONAL NOTES. 
1. Raspail's Description of the Structure of Polypes. 
" I have pointed out that the polypus is nothing but the continuation of its 
case, which becomes bony or cartilaginous in the lower part, in proportion as 
the upper part is developed. Consequently its tube, or rather its involucrum, 
instead of being a shapeless transudation from its body, is formed by successive 
additions of epidermoid membranes applied over each other in proportion as 
they are successively ossified. I have pointed out also that these polypi are 
merely microscopic fixed Cephalopodes, having, like the large- species of this 
genus, a bag which is contained within the tube, an excrementitial funnel, ovaries, 
an intestinal canal with similar curvatures, and a head with all its accessories 
equally corresponding ; so that, if the Sepia, for example, instead of having the 
dorsal part of its large bag ossified, had undergone the same change over the 
whole external circumference of this organ, and if its base had been fastened by 
an adhesive substance to a rock, it would have been exactly a gigantic polypus." 
New System of Org. Chem. p. 281-2. Obs. The species on which Raspail 
made these curious observations are not mentioned in the work from which the 
extract is taken : they seem applicable only to the ascidian polypes. 
2. Dr Grant's Account of the Ova of the Flustrce. 
" Although the ova of Flustrse have been often observed, no one appears to 
have hitherto examined either their mode of formation within the cells, or their 
mode of developement after expulsion, so as to determine the real nature of these 
globular bodies, and the erroneous conjectures of naturalists respecting them have 
greatly perplexed the history of this genus. The ova of the F. carbasea make 
their first appearance as a small yellow point, a little below the aperture of the 
cell, and behind the body of the polypus ; they are unconnected with the poly- 
pus, and appear to be produced by the posterior wall of the cell, in the same man- 
ner as the axis, or common connecting substance of the polypi, produces them in 
other zoophytes. In this rudimentary state, they are found in the same cells 
with the healthy polypi, but, before they arrive at maturity, the polypi of such 
cells perish and disappear, leaving the entire cavity for the developement of the 
ovum. There is never more than one ovum in a cell, and it occupies about a- 
third of the cavity, when full grown and ready to escape. When first visible 
it has a round or slightly oblong and regular form ; when mature, it is ovate with 
the small end next the aperture of the cell. The ova do not appear in all the 
cells at one time, nor is there any discernible order as to the particular cells 
which produce ova, or the part of the branch which contains them. Cells con- 
taining ova are found alike on every part of the branches, from the base to with- 
in two or three rows from the apex, occupied only by young polypi. Some- 
times we find half a dozen or a dozen of contiguous cells all containing ova, 
sometimes two or three only; and ofron such cells occur singly, at short and 
