'S93-J 77 [Hyatt. 
various names, not only accelerated development but every possible 
modification of this ; thus we find "concentrated," "abbreviated," 
"shortened," "omitted," all applied to tlie same effects. It is^ 
therefore, time that it should receive accurate sciejitific desig-nation. 
The term Tachygenesis from Tdxt»'s, meaning quick or speedy, 
is therefore proposed, and the original title "law of acceleration" 
should become the descriptive, popular term. 
Professor Cope has given the fullest explanation of this law but 
has joined it with retardation. Thus from his point of view, if I 
rightly understand him, inexact p.irallelism in development or 
failure to reproduce any hereditary characteristics is due to a ten- 
dency which appears in organisms and works in parallel lines Avith 
acceleration. The law being in his conception of a double nature, 
thus he says on page 142 of his "Origin of the fittest," "The 
acceleration in the assumption of a character, pi-ogressing more 
rapidly than the same in another character, must soon produce, in 
a type whose stages were once the exact parallel of a permanent 
lowej- form, the condition of inexact parallelism. As all the more 
comprehensive groups present this relation to each other, we are 
compelled to beheve that acceleration has been the principle of 
their successive evolution during the long ages of geologic time. 
Each type has, liowever, its day of supremacy and perfection of 
organism, and a retrogression in these respects h;is succeeded. 
This has no doubt followed a law the reverse of acceleration, which 
has been called retardation. By the increasing slowness of the 
growth of the individuals of a genus, and later and later assumption 
of the characters of the latter, they would be successively lost. 
To what power shall we ascribe this acceleration, by which the 
first beginnings of structure have accumulated to .themselves 
through the long geologic ages complication and power, till from 
the germ that was scarcely born into a sand lance, a human being- 
climbed the complete scale, and stood easily the chief of the 
whole?" And again on page 182 of the same work : '■•Acceleration 
signifies addition to the number of those repetitions during the 
period preceding maturity, as compared with the pi-eceding gener- 
ation, and retardation signifies a reduction of the numbers of such 
repetitions during the same time." Thus from Cope's point of 
view tachygenesis is the law of progression, and retardation is the 
law of retrogression, and they are both essential parts of his law 
of acceleration and retardation. 
