426 The American Naturalist.. [May, 
One aspect of the variation problem of to-day may, there- 
fore, be stated thus: What is the cause, nature, and extent of 
ontogenic variations in different stages of development, and 
under what circumstances do ontogenic variation become 
phylogenic? 
This brings us to an analysis of ontogenic variations in the 
plane of time as provisionally expressed in the following 
table :— 
ORIGIN OF VARIATIONS DURING LIFE HISTORY. 
Ontogenic Variations. 
(a) Gonagenic, i. e., those arising in 
the germ-cells, including the ‘ Blasto- 
genic’ tn part of Weismann, the ‘ Pri- 
mary Variations’ of Emery. 
(b) Gamogenic, i. e., those arisin 
during maturation and fertilization, 
including the ‘ Blastogenic’ in part of 
Weismann, ‘Secondary,’ or ‘ Weis- 
mannian variations’ of Emery. 
(c) Embryogenic, i. e., those occur- 
ring during early cell division, in- 
cluding the ‘ Blastogenic’ and ‘ Soma- 
togenic’ in part of Weismann. 
(d) Somatogenic, i. e., those occur- 
ring during larval and later develop- 
ment after the formation of the germ- 
cells. 
B. Phylogenie Variations. 
heredit 
Theories of Causation. 
Theoretically connected with patho- 
logical, nutritive chemico-physical, ner- 
vous influences, as implied by Kölliker 
and others, including the doubtful phe- 
nomena of Xenia and Telegony. 
gony 
Theoretically connected with influ- 
ences named above, also with the com- 
bination of diverse ancestral characters, 
‘Amphimixis’ of Weismann. 
Theoretically connected with exten- 
sive anomalies due to abnormal segmen- 
tation and other causes, as observed in 
the. mechanical embryology of Roux, 
Driesch, Wilson, and others. 
Connected with reactions between the 
hereditary development forces of the in- 
dividual and the environment. 
Variations from type originating in any of the above stages which become 
itary. 
The above table illustrates limits which certainly should 
not be sharply drawn between the successive stages of onto- 
geny, although intermediate focal points of real distinction 
must exist. The four terms proposed are not in the sense of 
the ‘ blastogenic’ and ‘somatogenic’ of Weismann, for there is 
no implication of his petitio principi, namely, of the separation 
of the hereditary substance or specific germ-plasm from the 
body-cells. Even before somatogenic separation has taken 
