311 
is also perfectly conceivable that the morphology of the individual cells 
in the row might differ after the acquisition of the new character (in so 
far as this assumption is required by recent cytological studies), and yet 
not a single organ or part of the organism be different up to the stage in 
ontogeny when the new character appears. Unless, therefore, a change in 
the energies of the cells inevitably necessitates a change in the morphology 
of all the cells or of all the organs which they compose, the argument of 
Montgomery proves nothing. 
As to the argument of His and others, that the supposedly ances- 
tral stages are merely the physiologically necessary stages in the develop- 
ment of the individual; it again, as Griggs points out, confuses mor- 
phology with physiology, and is open to the further objection that it is 
directly opposed to the facts. Why, for example, should the condition of 
perfect blindness, with complete loss of all the essential structures of 
the eye, be attainable only by the round-about way of first developing the 
foundations of a normal eye? Why should a serpulid be able to regenerate 
a perfect operculum in a manner entirely different from, and even opposed 
to the ontogenesis of the organ, if there is any physiologically necessary 
way in which that particular individual or that particular organ must 
develop? The thing that makes it necessary for development to take a 
certain course in a given individual is the fact that the development has 
taken* that same course in the ancestors. ‘This species of coercion may, 
to be sure, be relaxed, and the development take some other course, but 
it is usually relaxed with extreme slowness, and after many generations 
have passed. 
If inheritance were perfect, the individual would take exactly the 
same course in development as its ancestors. That it does not do this 
in all cases is, as Griggs points out, a more remarkable fact than that in 
other cases it should follow the ancestral mode of development so closely. 
Griggs explains the loss of inheritance as due to a progressive condensa- 
tion of the ontogeny by the “omission of more and more of the super- 
fluous ancestral stages.” This is the well-known law of acceleration or 
tachygenesis. Like most embryologists, however, he misconceives the law, 
as shown by the foot-note quoted above. Embryologists are especially 
prone to limit the law of acceleration in development to the skipping or 
omission of steps, and the consequent shortening of development. This is 
not in keeping with the views of Hyatt, who first definitely formulated 
the law; and, as all paleobiologists know, it is not in keeping with the 
