310 Scientific Intelligence. 
bryonic and adult type, leaving no doubt that the one is descen 
from the other. This relation was termed exact parallelism. It 
t was then shown that the inexact parallelism was the resu 
unequal acceleration or retardation ; that is, acceleration affecting 
one organ or part more than another, thus disturbing the comb 
nation of characters which is necessary for the state of exa L 
lelism between the perfect stage of one animal and the 
to the parts of an animal, while retardation implies con inual st 
i y has also show? 
(Method of Creation, 1871), that the additions either appeared 3° 
: 8 ifie Jd f the 
trine of evolution in his Gastrea theory. Prior to this generaliza- 
tion, it had been impossible to determine the true relation existing 
h, or, to speak other- 
t. 
of growth (or segmentation) in all of the types of eggs, the 
ot i a; ee beyond ‘which the identity a 
Not that the four types of gastrula are without difference, _— 4, 
difference may be accounted for, on plain principles. In gee 
Heckel, in his “ Anthropogenie,” recognizes the importance © 
