16 HISTORY OF THE HUMAN BODY 



are called c&nogerietic, or modern, are clearly of no importance 

 in such inquiries as the present, and must be carefully distin- 

 guished from those that are palingenetic, that is, actual repe- 

 titions of past history. 



It is essential, then, in order to interpret correctly the two 

 records, phylogenetic and ontogenetic, and from them to re- 

 produce the past history of our race, with its solutions of the 

 details of man's structure, that the nature of 'each form of 

 record be thoroughly understood. The phylogenetic or race- 

 history is the plainer and more direct of the two, and presents 

 fewer technical difficulties to the student, but it contains at 

 present extensive gaps, not yet filled in by the discovery of 

 fossil remains; the manuscript is plain and clear, but has suf- 

 fered much from the ravages of time and is fragmentary at 

 best : the ontogenetic, on the other hand, presents a more con- 

 tinuous story, but the difficulties in the way of investigation 

 are very great; here the manuscript is written in a micro- 

 scopic hand, and is, moreover, a palimpsest, scribbled over with 

 extraneous material, added at late dates and connected with 

 the exigencies of development. 



The characteristics of the phylogenetic record may be made 

 clear by the aid of the accompanying diagram [Fig. 6], which 

 represents a purely hypothetical case, and the conditions in- 

 volved may be presented in the form of laws, as follows : 



I. Development has not been in a single direction, but in 

 many, since the constant rivalry between allied forms causes 

 them to continually push their vvay into neiv environments, 

 the gradual adaptation to which causes a greater and greater 

 divergence between the descendants of those that entered the 

 new environment and those that remained in the old. 



To illustrate this by the diagram, suppose 29 to represent a 

 terrestrial carnivorous animal, living on the border of the 

 ocean and preying upon the forms of life found upon the 

 shore, or within shallow water. Pressed by the struggle for 

 existence, in this instance represented by the scarcity of this 

 sort of food, certain individuals venture farther out into 

 deeper water and attempt to capture fish. Thus begins the 



