686 The American Naturalist. [August, 
and.anterior premolars in the Mesozoic and most of the Terti- 
ary Mammals (excepting some Ungulates) points, however, 
very decidedly to the conclusion that the want of definition 
between these teeth in many of the modern Jnsectivora is an 
acquired feature.” I quote this passage from Flower and 
Lydekker, because an important paper by Leche has lately ap- 
peared in which he claims that the milk teeth represent an 
earlier development phase than the permanent teeth. He ar- 
rives at this generalization from a study of the milk dentition 
of the Lemurs, including Tarsius. Leche finds, for example, 
that in the anterior milk dentition of Adapis magnus the milk 
canines are much reduced in size, and more resemble the form 
of the premolars, and he also points out that the deciduous 
dentition of this species of Adapis very closely resembles the 
permanent condition of Adapis parisiensis. Leche concludes, 
therefore, that A. parisiensis represents the most primitive and 
ancestral form of Adapis known, and that the Ape-like form of 
the incisors and canines of A. magnus is a secondary condition 
derived from that of Adapis parisiensis. I feel confident that 
paleontologists will not accept this dictum in regard to the 
significance of the milk dentition as expounded by Leche. I 
should like to notice one point that seems to contradict this 
general law as deduced by Leche. In Tarsius, for example, 
Leche’s figures plainly show that the upper milk canine 
is larger than either of the milk incisors or the anterior 
premolars. If the structure of the anterior milk teeth is to be 
our guide in determining the evolution of the Lemurs, then 
Tarsius has come from a type which had large canines and in 
which these teeth were erect and of greater size than either the 
incisors or premolars. This conclusion corresponds better with 
the paleontological record. 
One of the best examples of extreme specialization and re- 
duction in the size of the canines is the case of the Anoplother- 
idx, an extinct family of Artiodactyle Ungulates. In this 
group the dentition is closed and the canines are of the same 
size and structure as the anterior premolars. I am sure that 
no paleontologists will claim that the dentition of the Anoplo- 
theridæ is primitive, as the whole structure of this family de 
