110 B. G. Wilder on a foetal Manatee and Cetacean. 
paring their structure with these embryonic stages. * * * As 
the young of the frog (tadpole) has the tail and form of a sala- 
mandrian, therefore the salamanders are higher than the frogs.” 
(20, 592. 
In accordance with the above rule, and upon the hypothesis 
of evolution, we should expect the embryo hippopotamus to 
resemble a manatee, and the embryo manatee to look “ very 
like a whale.” But since the young manatee has a head like 
an adult hippopotamus, we must either reverse the usual opin- 
ion as to the relative rank of the aquatic and terrestrial Ungu- 
lates, or qualify the rule above stated so as to meet the present 
case. 
This apparent discrepancy between generally accepted views 
as to the coincidence between rank and stages of devel- 
opment seems to be accounted for by the doctrine of Retro- 
grade metamorphosis, alluded to by Darwin (24) and Hyatt 
(26) and perbaps by other authors. 
The following passages from the “Origin of Species” are 
especially applicable. 
“The embryo in the course of its development generally 
rises in organization ; I use this expression, though I am aware 
that it is hardly possible to define clearly what is meant by the 
organization being higher or lower. But no one probably will 
dispute that the butterfly is higher than the caterpillar. In 
some cases, however, the maturer animal must be considered 
as lower in the scale than the larva, as with certain parasitic 
crustaceans,” (( 6.) 
‘Recent forms are generally looked upon as being on the 
whole higher in the scale of organization than ancient forms; 
* * * this fact is compatible with some forms having retro- 
graded in organization, by having become at the last stage of de- 
scent better fitted for changed and degraded habits of life.” 
(24, 426, also 402 and 397.) 
“Slight variations generally appear at a not very early 
period of life and are inherited at a corresponding not early 
period.” (24, 399 and 316. 
““ Whatever influence long-continued use or disuse may have 
had in modifying the parts of animals will chiefly or solely 
have affected them when mature * * * and the effect thus 
roduced will be transmitted to the offspring at a correspond- 
Ing mature age.” (24, 401. 
“ This process, while it leaves the embryo almost unaltered, 
continually adds, in the course of successive generations, more 
and more difference to the adult. Thus the embryo comes to 
be left as a sort of picture, preserved by nature, of the ancient 
and less modified condition of the animals.” (24, 316 and 403.) 
In other words, the idea of evolution, whether of individuals 
