POLYPS. 69 
organs may exist at the same time, and in variable number, in one 
and the same individual. And many other Polyps are also herma- 
phrodite. In others again the sexes are separate: whether both male 
and. female individuals occur on one and the same stem (Monecia, 
as in Plants), or one Polypstock bears only males, another only 
females (Diwcia). The last is the case of Veretillum. In the 
Bryozoa, Monecia appears to prevail universally, yet so that (to 
judge from the investigations of NorDMANN in Tendra zostericola, 
and of VAN BENEDEN in Alcyonella) the cells which contain Polyps 
with eggs are more numerous than those with spermatozoa. These 
peculiar constituents of the seed (vid. above, p. 43), of which the 
motions are so striking under the microscope, have, of late years, 
caused the important discovery of the sexual propagation of Polyps; 
but for them, ovaries alone would now, as twenty years ago, be 
ascribed to this class, especially as the seed-secreting organs (testes) 
are not to be distinguished in it, as to external appearance, from 
those that prepare the germs (ovaria)!. In those Anthozoa that 
have, like the Actinte, a cavity of the body distinct from that of 
the stomach, they are situated between or upon the partitions that 
divide that cavity into cells (see above, p.67). In Sertularia and 
Campanularia most of the Polyps are without sex, whilst cells with 
ova are developed in the axille of the branches. 
Propagation by spontaneous division does not occur in most 
Polyps. In Caryophylla there is a complete longitudinal fission, 
occasioning the dichotomous form of the Polypary, since two Polyps 
come from.one, four from two, &c. If the longitudinal fission be 
incomplete, cells of irregular form arise, as in Meandrina. 
In most Polyps the power of reproduction is very great. TREM- 
BLEY’S experiments on the fresh-water Polyp are well known: he 
divided them longitudinally and transversely, and every piece 
formed a new animal?> Roxrsen found that even the tentacles or 
1 Such is the case also in Mollusca, nay even in some fishes ; and in general the 
sexual organs in the animal kingdom possess a similarity in the two sexes, which was 
observed by the ancients, and occasioned many fanciful appellations and comparisons. 
2 Hence Linn&us borrowed the name Hydra for this animal genus, from a com- 
parison with the Hydra of mythology : 
...ab upso 
Ducit opes animumque ferro. 
Horat, Od. tv. 60. 
