294 THE POPULAR SOIENCE MONTHLY 
In the matter of the succession of teeth the follicles which form the 
last two—the milk premolars—form tecth in the first set of a totally 
different and usually more advanced character than the teeth to be 
formed from the same follicles in the permanent set. As a general 
thing then the conclusion would be that the milk teeth tend to have 
the same characters as mark the permanent set, but when they vary 
they often retain characters of the phylogenetically ancestral form. 
Weber adds that the later the succession the less the difference between 
the milk and permanent sets. 
Turning to the limbs, there are again several distinctly ontogenetic 
characters, which are by no means ancestral. First, the formation of 
epiphyses, so that a bone ossifies from three or more centers. This is 
purely an ontogenetic adaptation and has no phylogenetic significance. 
Then the articular ends of all the limb bones are greatly enlarged as 
compared with adults. This again is not phylogenetic but an adapta- 
tion, the joints and their ligaments being early approximated to their 
permanent conditions. Then the length of limbs seems to be ef- 
fected as an embryonic adaptation. First take the case of man born 
with disproportionately short arms and legs. The legs have been inter- 
preted as representing a phylogenetic condition, but the same rule does 
not apply to the arms which were ancestrally long. This feature of 
short limbs is also characteristic of carnivora and IJ feel that it is an 
embryonic adaptation; certainly the ancestral limb can not be deduced 
from the young condition. Quite the reverse of conditions obtains 
among the Ungulata where the young at birth have disproportionately 
long limbs, which with equal certainty does not represent any ancestral 
condition recapitulated, for the ancestral limb in ancestral forms is 
shorter. Again, I believe the anomalous legs are adaptations to either 
the necessity for speed on the part of the young, or for height to reach 
the teats, suckling being while the parent is standing. 
In the cases of the reduction of digits, greater portions of the re- 
duced digits are usually found in the young animals than in the adults, 
but in the case of the entire loss of a digit it is also lacking in the 
young and embryo. 
The general conclusion of the whole matter would then be that the 
young give us very little which is not deceptive in reconstructing an- 
eestral forms. In certain cases, namely in the teeth and in reduction 
of digits, confirmatory points may be obtained, but these must be 
used with care, the valuable constructive evidence being rather found 
in adult skeletons, and in morphological comparisons. While allowing 
that many stages are recapitulated in the development of an individual, 
the vast number of adaptations impressed on the young to be used after 
birth, make their skeletons specialized even from birth, and such dif- 
ferences as exist are seldom reminiscent. 
