816 General Notes. {August, 
ment of certain considerable groups, every addition to that 
knowledge demonstrates that what has appeared to be excep- 
tional or in violation of general principles, upon further investi- 
orms. 
The Chordata present three well-marked modes of embryonic 
development consequent mainly upon the manner in which the 
germinal matter of the egg is related to the vitellus, and upon 
how much the latter takes part directly in the formation of the 
embryonic organs, and in what manner the blastula or blasto- 
phere is directly related to its environment in the course of its 
development and growth. The direct influence of conditions 
which induce modifications in a purely mechanical manner is very 
plainly illustrated in embryological development ; in fact it may 
be shown that the highest type of development as displayed in 
- the greatest complexity of the germ or embryo has grown out 0 
a simpler condition developing under simpler environing condi- 
tions. It may thus be shown that even the mode of development 
the ovum has been modified through adaptation. 
I. The lowest and most unmodified expression of chordate 
