DEVELOPMENT OF ECHINODERMATA. 565 
have brought to light a most remarkable set of facts in regard 
to the developmental history of the Echinodermata. The 
details of this history vary so greatly in the different sections 
of the group, that all which can be here attempted is a 
general notice of its most important features. The em¬ 
bryonic mass of cells, which is produced in the ordinary way 
from the egg, is usually converted, not (as in Insects) into a 
larva which is subsequently to attain the perfect form by a 
process of metamorphosis, but into a peculiar being, destined 
to a merely temporary existence, whose function seems to be 
to give origin to the real Echinoderm by internal gemmation, 
to obtain and prepare for it the materials of its development, 
and to carry it to a distance from its fellows, so as to prevent 
the spots inhabited by the several species from being over¬ 
crowded by the accumulation of their progeny. These larval 
zooids present many points of resemblance to the larvae of 
certain Annelids; their bodies have a bilateral not a radial 
symmetry, the two sides being exactly alike; each side 
Fig. 305.— Pentacrinoid Larva of Comatula. Fig. 306.— Comatula. 
is furnished with a ciliated fringe along the whole or the 
greater part of its length; and the two fringes are united 
by an upper and a lower transverse ciliated band, between 
which the mouth of the zooid is situated. Although the 
adult Star-fish and Sand-stars have neither intestinal tube nor 
