HYDROIDEA. 23 
may be early distinguished within them, and are often arranged 
along a central axis, each communicating, according to Lister, with 
the common axis of the zoophyte.* My associate, Dr. Charles 
Pickering, first pointed out to me, while at sea, in 1838, that a close 
analogy subsists between the arrangement of the ovules in a vesicle 
and a contracted branchlet of the 
zoophyte.t ‘The same subject 
has been thoroughly investigated 
by Professor E. Forbes, and the 
fact of this arrangement fully 
ascertained.t In consequence of 
the communication with the axial 
cavity of the zoophyte, the pulpy 
chyloid fluid of the main stem 
and branches is carried into the 
vesicle and to each ovule, and the developement of the whole pro- 
moted. On arriving at maturity, the ovules pass out in succession 
from the sac, which, now empty, falls off. They are carried about 
for awhile by means of their vibratile cilia, and then—perhaps in two 
or three days—they affix themselves. Each now grows and buds, 
till shortly “a whole grove of Corallines” is formed. 
According to Van Beneden, the Campanularide, when first deve- 
loped from the ovule, are like minute Meduse in shape, and have 
eight eyes, which are lost as the animal attaches itself. In this state, 
it has no vibratile cilia.) This same author has very minutely in- 
vestigated the Tubularide, and finds in them the same mode of 
developement, and eight eyes to the medusa-shaped young, at the base 
of the tentacles. Dalyell seems to have observed similar facts. He 
states that the ovules, which in this group are collected about the 
bases of the tentacles, drop from their attachment for evolution below. 
Slight prominences soon denote incipient tentacles; next the nascent 
animal reversing itself, enjoys the faculty of progression by means of 
the inverted tentacula, as on so many feet, apparently to select a site ; 
when again resuming the natural direction, with the extremities up- 
wards, the lower surface fixes itself below and roots there for ever. |i 
Fig. 7. Ta Fig. 8. 
Plumularia. Sertularia. 
* J. J. Lister, Phil. Trans., 1834, pp. 365-389, pl. ix. and x. 
+ Figures 7 and 8 are by Dr. Pickering; they were drawn from gulf-weed species, in 
September of 1838, at the time the above-mentioned observation was made, 
+ Proceedings of the British Association, for 1844, 
§ Van Beneden, Mém. sur les Campanulaires, &c. Brussels, 1844. 
|| Rep. Brit. Assoc., for 1834, p. 600. 
