232 FOOT-NOTES TO EVOLUTION. 
biogenetic law, in his formula, “ Gleichung zwischen der 
Entwicklung des Embryo und der Thierreihe,” com- 
parison of development of the embryo with the race of ant-. 
mais, But Louis Agassiz, although not the discoverer, 
was undoubtedly the first to use the law as an aid in 
the systematic study of biology. While he regarded the 
various genera, not as ancestors and descendants, but 
as progressive steps in creation, still he saw the analogy 
between the stages of growth of the individual and 
these progressive steps. It was reserved for Alpheus 
Hyatt to formulate the law and to strengthen theory 
with practical examples based on the study of cephalo- 
pods.* In his later papers Professor Hyatt has given a 
more exact and comprehensive definition of the law 
of acceleration or ¢achygenests: “ All modifications and 
variations in progressive series tend to appear first in 
the adolescent or adult stages of growth, and then to be 
inherited in successive descendants at earlier and earlier 
stages, according to the law of acceleration, until they 
either become embryonic or are crowded out of the 
organization and replaced in the development by charac- 
teristics of later origin.” | A still more definite state- 
ment by the same author is the following: “ The sub- 
stages of development in ontogeny are the bearers of 
distal ancestral characters in inverse proportion and of 
proximal ancestral characters in direct proportion to their 
removal in time and position from the protoconch or 
last embryonic stage.” { Since Hyatt’s first paper the 
* A. Hyatt. Mem. Boston Soc. Nat. Hist., vol. i, 186667; 
and Proc. Boston Soc. Nat. Hist., vol. i, 1866, Parallelisms of In- 
dividual and Order among the Tetrabranchiate Mollusks. 
+ A. Hyatt. Smithsonian Contribution to Knowledge, No. 
673, Genesis of the Arietide, Preface, p. ix. : 
$ Proc. Am. Phil. Soc., vol. xxxii, No. 143, A. Hyatt, Phy- 
logeny of an Acquired Characteristic, p. 405. 
