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598 LAWS OF ORGANIC DEVELOPMENT. 
In this table we see a decline in the number of teeth of the 
higher groups. Thus the premolars are one less than the nominal 
number in the whole order, and they lose one in each jaw in the 
Old World apes, and man. he molars maintain the normal num- 
ber throughout, but the third in both jaws is in the Simiade re- 
duced by the loss of a fifth or odd tubercle, thus becoming four- 
lobed. In the upper jaw this is first lost in the Semnopithecus ;. 
in the lower, in the next highest genus Cercopithecus. In Homo 
its appearance is “retarded,” the interval between that event and 
the protrusion of the second molar— six to ten years — being rela- 
tively greater than in any genus of Quadrumana. Its absence is 
then the result of continued retardation, not of a new and adap- 
tive suppression, and is of direct systematic zoological value. 
In the incisors a reduction is also plainly visible, as we pass 
from the most completely furnished Lemuride to the genus Homo. — 
One from the upper jaw is first lost, then in the Cebide, one from 
the lower also. The number remains the same through the Simiade 
and normal Hominide, but in the abnormal cases cited the process 
of reduction is continued and another incisor from each side dis- 
appears. That this also is truly “retardation” is also evident 
from the fact that the exterior incisor is the last developed, being 
delayed in ordinary growth a year later than those of the inner 
pair. The same retardation is seen in the quadrumane Cheiromys 
(the Aye-aye), and the whole order Rodentia. In the latter, the 
rare presence of the reduced second incisors shows that here also 
the external incisors are lost. This retardation is also of system- 
atic importance, and, should either of the characters described be 
constant in any of the species of the genus Homo, would at once 
entitle it to new generic rank. The very frequent absence of the 
posterior molars (wisdom teeth) has been recently found to char- 
acterize a race in India. Should this peculiarity prove constant, 
this race would with propriety be referred to as a new genus of 
Hominide, as we’ have many cases of very similar species being 
referabie to different genera. It is altogether probable that such 
will, at some future time, be the condition of some race or races 
of men. 
II. ON THE LAWS OF EVOLUTION. 
Wallace and Darwin have propounded as the cause of modifica- 
tion in descent their law of natural selection. This law has been 
