PROGRESS OF MICROSCOPICAL SCIENCE. 
155 
the organizing phenomena is in the multiplication of the fertilized 
embryo-cell, and its conversion into continuous organized strata, by 
further histological changes in which the morphological foundations 
of the future embryo or new being are laid. 
“ I need not now recur to the further series of complications in the 
formative process by which the bilaminar blastoderm is developed, and 
becomes trilaminar or quadrilaminar, but only recall to your recol- 
lection that while these several states of the primordial condition of 
the incipient animal pass insensibly into each other, there is a per- 
vading similarity in the nature of the histological changes by which 
they are reached, and that in the production of the endless variations 
of form assumed by the organs and systems of different animals in the 
course of their development, the process of cell production, multipli- 
cation, and differentiation remains identical. The more obvious mor- 
phological changes are of so similar a character throughout the whole, 
and so nearly allied in the different larger groups, that we are led to 
regard them as placed in some very close and intimate relation to the 
inherent properties of the organic substance which is their seat, and 
the ever-present influence of the vital conditions in which alone these 
properties manifest themselves. 
“ The formative or organizing property, therefore, resides in the 
living substance of every organized cell and in each of its component 
molecules, and is a necessary part of the physical and chemical con- 
stitution of the organizing elements in the conditions of life ; and it 
scarcely needs to be said that these conditions may be as varied as the 
countless numbers of the molecules which compose the smallest 
particles of their substance. But, setting aside all speculation of a 
merely pangenetic kind, it appears to me that no one could have 
engaged in the study of embryological development for any time 
without becoming convinced that the phenomena wdiich have been 
ascertained as to the first origin and formation of textures and organs 
in any individual animal are of so uniform a character as to indicate 
forcibly a law of connection and continuity between them ; nor will 
his study of the phenomena of development in different animals have 
gone far before he is equally strongly convinced of the similarity of 
plan in the development of the larger groups, and, to some extent, of 
the whole. I consider it impossible, therefore, for anyone to be a 
faithful student of embryology, in the present state of science, without 
at the same time becoming an evolutionist. There may still be many 
difficulties, some inconsistencies, and much to learn, and there may 
remain beyond much which we shall never know ; but I cannot 
conceive any doctrine professing to bring the phenomena of embryonic 
development within a general law which is not, like the theory of 
Darwin, consistent with their fundamental identity, their endless 
variability, their subjugation to varying external influences and con- 
ditions, and wuth the possibility of the transmission of the vital 
conditions and properties, with all their variations, from individual 
to individual, and, in the long lapse of ages, from race to race. 
“ I regard it, therefore, as no exaggerated representation of the 
present state of our knowledge to say that the ontogenetic develop- 
