B. G. Wilder on a fetal Manatee and Cetacean. 109 
semblance. 
It is admitted by nearly all that the anatomical resemblances 
upon which affinities are recognized are much greater between 
the Sirenia and certain Ungulata than between either of these 
groups and the Cetacea. 
There would seem to be reason, therefore, for attaching very 
considerable taxonomic value to the fact that the head and face 
g and horse. — 
obable ancestors of the Sirenia.—In the discussion of this 
m eg of a purely ideal signification. : 
t is an almost universally accepted rule that the earlier 
stages of animals resemble the permanent conditions of lower 
forms. This is stated by Dana as follows: “As a species in 
development passes through successive stages of i ae rela- 
ive grade in inferior species may often be determined by com- 
*I use these terms for conveni not because I them as 
tng tiaiera : convenience and regard express- 
