SOME PROBLEMS OF COELENTERATE ONTOGENY Rae 
as yolk granules, which can only become available by the dis- 
solution of the cells which contain them. Supposing that origin- 
ally it was equally distributed, it could only remain so by the fur- 
ther assumption that cell division was likewise equal and contin- 
uous throughout. This we know is seldom the case, being in 
general inversely as the amount of yolk varies. Hence those 
cells whose growth and metabolism became more rapid would 
first exhaust their own deutoplasm and demand supplies from 
outside. And here must originate the struggle among cells 
_ which has been emphasized above. 
Assuming the substantial truth of the conception we must 
face the implication that the older views as to the ontogenic 
and phylogenic significance of the germ layers are discredited 
by these further facts, as they have also been in theory. I be- 
lieve we may, therefore, conclude that fundamentally the phe- 
nomena involved in germ-layer formation are primarily physio- 
logical processes, and relate to protective, motor, and nutritive 
ends; and that only secondarily, if at all, can they be supposed 
to have any significance in ontogeny or phylogeny. 
REVIEW AND DISCUSSION 
As stated in an early section of this paper one of the purposes 
in view was to review certain phases of current and earlier theory 
and doctrine concerning problems of ontogeny, in the light of 
recent knowledge, and to seek to point out and correct such errors 
as may easily come within the scope of pertinent discussion. 
This seems to the writer particularly important and desirable 
just at this time of virile criticism and readjustment. 
For some time the conviction has grown that not a few of the 
earlier views and theories touching ontogenetic problems had 
outlived their days of service, and that new facts were demanding 
new methods of interpretation. For example, who today pre- 
tends to invoke, in its original content, the Recapitulation Theory 
in correlating ontogeny and phylogeny? Who would seriously 
defend, or use the so-called laws of cleavage in interpreting every 
phase of egg development? And so one might multiply examples. 
