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It happens that certain characters of these formerly-adult 
stages are suppressed in the embryonic and infantile stages, 
although the other features of these formerly-adult stages are 
faithfully reproduced. Such phenomena may be explained by 
supposing that such suppression was due to a modifying or 
controlling action guided by the requirements of the individual ; 
and that such action was therefore adaptive, and to the advan- 
tage of the individual at the time. These ideas may be ex- 
pressed as follows :— 
“ The embryonic and infantile stages may not always exhibit 
all the characters of the stage of development of which they should be 
the morphological representations, but they may only exhibit such 
features as are suitable to the individual’s requirements, sup- 
pressing those unsuitable, especially when such suppression, whether 
temporary or permanent, is to the advantage of the individual on 
the score of economy.” 
The conclusions now arrived at may be summed up as 
follows :— 
So far as the conditions of environment allow, the offspring 
tends during development to exhibit the various phases of its 
parent’s life at an earlier age than the parent exhibited them*— 
the tendency to earlier exhibition increasing in proportion to 
_ the lateness of the character; that the offspring tends to 
direct development by eliminating dissimilar stages of growth 
on the score of economy; and for the same reason it is wont to 
suppress or modify, in its embryonic and infantile stages, 
_ characters unsuitable or not absolutely necessary to its develop- 
_ ment at the time. 
PROGRESSION AND RETROGRESSION OF DEVELOPMENT. 
Developmental variations may be divided into progressive 
and retrogressive, as Ammonites very conclusively shew. 
When a phylogenetic series is developing successive new 
: *In the case of one or a few generations the “earlier inheritance’? may 
_ be practically disregarded. Heredity may be summed up as “Ontogeny should 
repeat ontogeny.” 
