304 EMBRYOLOGY AND CLASSIFICATION. 
another, and that their different modes of de- 
velopment may lead from one to the other. 
Thus far Embryology has not recorded one fact 
on which to base such doctrines. 
In Radiates, as soon as the young is formed, 
it is a spheroidal, radiated animal, exhibiting 
from the beginning, in all the three classes of 
this primary division, — Polyps, Acalephs, and 
Echinoderms, — the general plan of structure so 
characteristic of the Radiate type, and so distinct 
from all others. Let us first see what inference 
may be drawn from the development of the lower 
representatives of this type; even though I can 
only allude here very generally to facts which 
could not be stated more at length without a 
great deal of illustration and detail. The young 
Polyp reaches its mature condition through a 
succession of changes, which, when compared 
with the structural complication of the adult 
representatives of the different orders in this 
same class, promise to furnish better data for the 
classification of these animals than have ever 
been obtained heretofore. The various modes 
of increase observed among Astreans, and espe- 
cially among Fungide, already show that the 
families in which independent animals complete 
their growth, without forming compound com- 
munities, are inferior to the compound ones; 
while those in which one diameter prevails over 
