158 TRANSACTIONS OF THE [MAR. 5, 
side of embryology, as to the transmission of acquired char- 
acters. Complex structures occur in early stages, which en- 
tirely disappear in later development before the develop- 
ment of a nervous system. Can these structures of one 
stage be transmitted by another? That the germ plasm is 
not to be directly operated upon by external stimuli seems 
proven experimentally. The removal of the hypoblast of Ech- 
inoderm gastrula does not prevent the remaining germ layers 
from producing characteristic structures. These appear in no 
way modified by the loss of the tissue which contains the germ 
plasm. 
Dr. Wortman, continuing the arguments of Prof. Cope, 
referred to structures of the human foot, which come to be 
evolved because of pressure, as sesamoid bones, keels and ridges 
of the great toe. These structures he had found invariably 
present on examining 150 specimens of foetuses, while in no 
case was there a tendency to their formation in the lateral toes, 
where pressure causes were wanting. This evidence would mili- 
tate strongly against the doctrine of fortuitous variation. The 
plasticity of the harder animal tissue was emphasized—bone and 
teeth. Enamel is a living substance, partly regenerative, and 
capable of being impressed by mechanical causes. Degeneration 
is hardly to be explained from the standpoint of selection, 
especially under conditions of civilization, where selection 
should be inactive, e. g., as loss of wisdom teeth or of terminal 
phalanx of little toe. 
Prof. E. 8S. Morse emphasized the failure of evidence as to 
the transmission of acquired characters. He referred to the 
recent experiments of A. Agassiz, which showed that larval 
flounders preserve their symmetry when precluded from their 
normal living conditions. 
In concluding the discussion, Prof. Poulton explained that 
the variations upon which natural selection operated were at 
the beginning often most minute, and hence it would not seem 
amiss to regard selection as creative. On the other hand, he 
could not admit with Prof. Cope that selection regarded the 
causes of variation as unimportant. But it was not necessary 
