34 Heredity. 



ics of the biogenetic process, we must descend into the 

 deep obscurity of plastid-life, and search for its true 

 efficient cause in the motion of organic molecules (Plas- 

 tidule-Bewegung). 



^^In fine, this question remains to be answered, Are 

 we in a position, by the aid of comparison with analo- 

 gous phenomena of motion, to form a satisfactory pro- 

 yisional hypothesis regarding the true nature of the 

 plastidule motions which are hidden from our direct 

 observation? Oar hypothesis of perigenesis is an at- 

 tempt to answer this question in the affirmative. 



*^As we review, from the highest and most compre- 

 hensive point of view, the sum of the phenomena of 

 organic development, the most general result of our 

 survey is the conclusion that the biogenetic process 

 is a periodic motion, which we can best picture 

 to ourselves as a wave motion. Adherinsf at first to 

 facts which are beyond dispute, and which admit of 

 direct observation, we may commence with our own an- 

 cestry: either confining ourselves to the so-called his- 

 toric period, in which we can pass from man to man by 

 direct proof; or else following, by the methods of an- 

 thropogeny, our ancestry still farther back, through the 

 vertebrates to amphioxus, and through the group of in- 

 vertebrates to the gastraea, and at last to the amoeba 

 and the moner. In either case the course of develop- 

 ment (entwickelungsbewegung) of our series of ances- 

 tors can be most simply represented by a wave-line, in 

 which the individual life of each organism answers to a 

 single Avave. 



**If now we enlarge our field of view to embrace not 

 simply our own direct ancestry but the whole of our 

 blood-relations, w^e can make clear by a genealogical tree 

 their relationship to each other. As the history of the 



