306 EMBRYOLOGY AND CLASSIFICATION. 
the highest class in this division — the Echino- 
derms — made an exception to this rule, and did 
not agree with the other Radiates in its mode of 
development. Johannes Miller, one of the most 
eminent investigators of modern times, in a long 
series of memorable papers upon the Embryology 
of Radiates, has maintained that the larval con- 
dition of the young Echinoderm, so far from being 
homologous.with the early stages of development 
in the other classes, is essentially bilateral. It is 
true that there is in many of the Radiates some- 
thing akin to a bilateral symmetry, though it is 
always subordinate to the prevailing idea of radi- 
ation in the plan. This tendency is already quite 
perceptible in the highest order of the Acalephs, 
the Ctenophore, and becomes still more so in 
some representatives of the class of Echinoderms, 
the highest in this type. The resemblance of the 
larve of the Echinoderms to the Ctenophore had 
not escaped my notice; but during the past year 
my son has shown conclusively, in a series of 
microscopic investigations not yet published, that 
they are as truly radiated as the most circular or 
spheroidal of the type. The further growth of 
the young Hchinoderms, from the young Comatula 
(as far as its history is known in its pentacrinal 
condition) to the gradual transformation of the 
common Star-Fish, with its undivided circular 
outline, with its two rows of simple ambulacral 
