ECHINODERMATA. 
759 
Towards this space the ca3cal intestinal process directs itself. It rises up 
througli it in the form of an elongated tubular closed papilla. The summit 
of the papilla is finally absorbed, and a patent anal opening is formed. 
The pseudembryo attains its mature form in from 3(5 to 48 hours. It is 
from 1'5 to 2 millims. in length, shaped somewhat like a kidney bean or a 
slipper, enlarged at the anterior extremity and somewhat contracted at the 
posterior. Its smooth structureless surface is studded with imbedded pale 
yellow oil-cells and covered with very small cilia. The four ciliated bands 
are still strongly marked, but the third (from the anterior extremity) has 
slightly changed its position. On one side of the body it has formed an arch 
forwards, its apex nearly touching the second band ; and in the wider space 
thus left between the third band and the fourth^ the pseudostome forms a 
deep involution of the sarcode, keyhole-shaped, richly ciliated, shallow an- 
teriorly, and deepening posteriorly into the short curved pseudocele, which 
merely dips under the fourth band, breaking through immediately behind 
it as a small round anal aperture. Behind the pseudoproct, and in the centre 
of the posterior extremity of the pseudembryo, there is a tuft of very long 
cilia, which moves with a peculiar rippling lash, and assists greatly in the 
locomotion of the zooid. The pseudembrj’^o moves rapidly in the water, rolling 
round and swinging from side to side ; as a rule, and especially when at rest, 
the surface bearing the pseudostome and pseudoproct is turned downwards. 
Very early in the development of the pseudembryo there is an accumula- 
tion of dark granules in the widest part, towards the anterior extremity ; and 
a few hours after the rupture of the vitelline sac two rows, one row superposed 
upon the other, each of five minute stellate spicules, appear in the sarcode- 
wall of the zooid round this granular mass, which now acquires a most dis- 
tinctly globular form. As the development of the pseudembryo proceeds, 
these spicules gradually expand till they form a delicately trellised basket of 
ten perforated plates entirely enclosing the granular globe. 
At the same time, from the point of meeting of the lower edges of the five 
plates of the lower row, a series of open calcareous rings curves downwards 
towards the posterior extremity of the pseudembryo, immediately within 
which, behind the pseudoproct, it ends in a round cribriform plate. Within 
each of these calcareous rings a hollow cylinder of parallel calcareous rods, 
united by cross trabeculae, now arises, the rods bound in the centre like a 
sheaf by the original ring. All the joints thus formed are placed end to end, 
but not connected, forming a jointed stem, supporting above the trellised 
basket, and abutting beneath against the terminal cribriform plate. 
The two tiers of plates are the oral and the basal plates of this pentacrinoid, 
plates which afterwards become absorbed or regularly modified. The rings 
with their enclosed calcareous sheaves are the joints of the stem of the pen- 
tacrinoid, and the cribriform plate finally forms its base of attachment. The 
skeleton of the pentacrinoid is thus mapped out within the body of the 
pseudembryo, while the latter still retains its full activity, its special organs, 
and its characteristic form. 
It is utterly impossible at this stage to trace the formation of the viscera 
of this young pentacrinoid, on account of the close calcareous netwoi-k in 
which the nascent organs are enveloped. From its colour and position, how- 
ever, there can be no doubt that the mass occupying the base of the cup 
represents the origin of the stomach, with its granular hepatic folds, while 
