DEVELOPMENT OF CORAL POLYPS. 83 
spermatic bodies rupture the walls of their respective glands 
situated on the fleshy partitions. As in Actinia, Lacaze- 
Duthiers thinks the fecundation of the egg occurs before it 
leaves the ovary, when also the segmentation of the yolk 
must take place. Unlike the embryo Actinia, the ciliated 
young of the coral, after remaining in the digestive cavity 
for three or four weeks, make their way out into the world 
through the tentacles. The appearance of the young, when 
first observed, was like that in Fig. 55, A, being an oval, 
ciliated gastrula with a small mouth and a digestive cavity. 
The gastrula changes into an actinoid polyp in from 
thirty to forty days in confinement, after exclusion from the 
parent, but in nature in a 
less time, and it probably 
does not usually leave the 
mother until ready to fix 
itself to the bottom. 
Before the embryo be- 
comes fixed and the tentacles 
arise, the lime destined to 
form the partitions begins 
to be deposited in the endo- 
derm. Fig. 55, C, shows the 
twelve rudimentary septa. 
These after the young polyp 
or ‘‘actinula’’ has become 
stationary, finally enlarge Fig. 55.—Development of a coral polyp, 
i Astroides calycularis. A, ciliated gastrula; 
and become j oined to the 2. young polyp with 12septa; C, D. young 
polyp farther advanced, with 12 tentacles; 
external walls of the coral ¢, the corallum and limestone septa begin- 
now in course of formation " a ae aati al 
(Fig. 55, C, c), forming a groundwork or pedestal on which 
the actinula rests. D represents the young polyp resting 
on the limestone pedestal. 
Lacaze-Duthiers found that the embryo polyp which had 
been swimming about in his jars for nearly a month, sud- 
denly, within the space of three or four hours after a hot 
sirocco had been blowing for three days, assumed the form 
of small disks (Fig. 55, B), divided, as in the Actinia, into 
twelve small folds forming the bases of the partitions within. 
Cc 
