188 ZOOLOGY. 
egg. When hatched, the larva is long, oval, and girded 
with four zones of cilia, with a tuft of cilia at the end, a 
mouth and anal-opening, and is about eight millimetres 
long. The body-cavity is formed by an inversion of the 
primitive layer which seems to correspond to the ectoderm. 
Within a few hours or sometimes days, there are indica- 
tions of the calcareous areolated plates forming the cup of 
the future crinoid. Soon others appear forming a sort of 
trellis-work of plates, and gradually build up the stalk, and 
Jastly appears the cribriform basal plate. Fig. 66, B, ce, rep- 
resents the young crinoid in the middle of the larva, whose 
body is somewhat compressed under the covering-glass. 
Fig. 180.—Antedon, stalked and free.—From Macallister. 
Next appears a hollow sheath of parallel calcareous rods, 
bound, as it were, in the centre by the calcareous plates. 
This stalk (B, c) arises on one side of the digestive cavity 
of the larva, and there is no connection between the body- 
cavity of the larva and that of the embryo crinoid. 
Two or three days after the appearance of the plates of 
the crinoid, the larva begins to change its form. The 
mouth and digestive cavity disappear, not being converted 
into those of the crinoid. The larva sinks to the bottom, 
there resting on a sea-weed or stone, to which it finally ad- 
heres. The Pentacrinus form is embedded in the larval body 
