22 PATTEN. [VoL. XII. 
views. But the latter usually tell the whole story, so that but 
few figures of sections have been deemed necessary. 
The amount of good material was so great that I have in no 
case used embryos for illustration if there was the least doubt 
of the abnormality being a real one, and not one due to post- 
mortem abrasion, shrinkage, or other causes of like nature. 
The present paper is an unexpected by-product of work 
along other lines. The time necessary for this digression 
from a prescribed course was somewhat grudgingly given. It 
is partly for that reason, and not because their value for this 
purpose was unappreciated, that I have not entered into a 
critical discussion of prevalent theories of heredity and devel- 
opment in the light of these new facts, although I have ventured 
to make a few suggestions of a theoretical character that natu- 
rally arose out of their consideration. 
It seemed to me that about everything of value in the way 
of argument has already been said and resaid on the various 
phases of epigenesis versws evolution. When the smoke from 
the volleys of words discharged in the last few years has 
cleared away somewhat, it will probably be found that the rival 
disputants are in closer agreement than has been suspected. 
But, after ail, the most convincing arguments are the plain 
solid facts. They are always eloquent, and we cannot have too 
many. One who has often had occasion to search the litera- 
ture on a given subject for definite information must be 
impressed with the uncertainties that hover thickly around the 
majority of observations, and which render them practically 
worthless for constructive purposes. 
While it is not claimed that the following descriptions are 
less open to this criticism than most others, it may be a point 
in their favor that, almost to the last, the embryos were selected 
and drawn with great care, merely as an illustration of isolated 
cases of variation, and without any preconceived ideas as to 
their meaning or mutual relations. 
It was my intention originally to publish a description of the 
normal development first, as I had abundance of material care- 
fully prepared and studied for this purpose. The reader would 
then be better able to appreciate the meaning of the abnormal 
