188 
THE DESCENT OF MAN. 
Part L 
passes through the same phases of embryological de- 
velopment. He retains many rudimentary and useless 
structures, which no doubt were once serviceable. Cha- 
racters occasionally make their re-appearance in him, 
which we have every reason to believe were possessed by 
his early progenitors. If the origin of man had been 
wholly different from that of all other animals, these 
various appearances would be mere empty deceptions ; 
but such an admission is incredible. These appearances, 
on the other hand, are intelligible, at least to a large 
extent, if man is the co-descendant with other mammals 
of some unknown and lower form. 
Some naturalists, from being deeply impressed with 
the mental and spiritual powers of man, have divided the 
whole organic world into three kingdoms, the Human, 
the Animal, and the Vegetable, thus giving to man a 
separate kingdom . 1 Spiritual powers cannot be com- 
pared or classed by the naturalist ; but he may endea- 
vour to shew, as I have done, that the mental faculties 
of man and the lower animals do not differ in kind, 
although immensely in degree. A difference in degree, 
however great, does not justify us in placing man in a 
distinct kingdom, as will perhaps be best illustrated 
by comparing the mental powers of two insects, namely, 
a coccus or scale-insect and an ant, which undoubt- 
edly belong to the same class. The difference is here 
greater, though of a somewhat different kind, than 
that between man and the highest mammal. The 
female coccus, whilst young, attaches itself by its pro- 
boscis to a plant ; sucks the sap but never moves again ; 
is fertilised and lays eggs ; and this is its whole history. 
On the other hand, to describe the habits and mental 
1 Isidore Geoffroy St.-Hilaire gives a detailed account of the position 
assigned to man by various naturalists in their classifications : 1 Hist. 
Nat. Gen.’ tom. ii. 1859, p. 170-189. 
