Son ROY L. MOODIE 
APPLICATION OF EMBRYOLOGICAL DATA TO PALEONTOLOGY 
It seems reasonable to state that the only way in which we 
can explain many paleontological facts is by reference to recent 
phenomena. We are seeking now to explain why, from the 
standpoint of development, the lateral-line system in ancient 
vertebrates is always associated with certain definite osseous 
elements. A suggested explanation is found in the manner of 
development of the lateral-line bones in Amiurus. It has not 
seemed necessary to investigate this condition in more than 
this one form, since from the work of Allis (’04) it is evident 
that there is a general conformity in the relationship of the 
bones of the head with certain portions of the lateral-line canals. 
Hence we are assuming that the phenomenon is constant in the 
larger aspects. 
We have seen that the lateral-line canals develop before the 
formation of bone. They are precocious structures which carry 
a mechanical influence into the formation of the skull for the 
following reasons: 
1. They introduce an inactive substance on which calcium salts 
may be deposited. | 
2. They attract the early deposition of bone because they fur- 
nish a more advanced state of colloidal substances on their sur- 
faces than is found elsewhere in the head except in those re- 
gions, such as the occiput, where the deposition of bone is brought 
about in response to stress. 
3. The lateral-line canals, because of their form, furnish a 
region for the influence of capillary and surface phenomena which 
are exerted in a purely mechanical way. 
4. The deposition of bone is not in response to the nervous 
stimulus of the sense organs, since bone is not deposited over 
them until later. 
If these explanations seem reasonable, it is possible to further 
explain our primary problem by stating that we have no reason 
to doubt that, in the larval stages of the Labyrinthodonts, the 
lateral-line sense organs and canals developed in the same preco- 
cious way they do now in modern fishes and that the canals 
exerted the same mechanical influence on the deposition of bone 
