572 MR ANDREW MURRAY ON THE PEDICULI 
something of this iridescence may be observed on the body of the Pediculi; but 
of more decided sculpture, or special marks, we can have little. The soft flexible 
skin allows what might be a hollow or depression in one case to be raised into a 
ridge or an elevation in another. The only parts which are sufficiently hard to 
retain their form under some degree of pressure are the legs and the antenne ; 
but unfortunately, in the insect world, these parts are usually so constant through- 
out all the species of a genus, that the existence of differences there seldom fail 
to indicate a different genus. We can only expect a very trifling amount of 
difference there, and this, when found to exist, must be reckoned of greater 
value than a larger difference in some more variable parts. After a careful 
search for decipherable characters, I have found the best in the form and pro- 
portions of the legs and claws, and more especially in the anterior legs and claws 
of the male, which are (as is frequently the case in all orders of insects) larger 
and more dilated than those of the female. 
Using these as characters, then, it is impossible to deny that there are toler- 
ably well-marked differences between the parasites of different races; and as in 
several of these races I have had the benefit of a large series of specimens, I am 
able to add that these differences are constant. A glance at the drawings (Plates 
XXIX. and XXX.), which have been made with every care and precaution by 
the aid of the camera lucida, will show the nature of these differences. The 
teeth of the claw vary considerably. In some, as in the European, the Caffre, and 
the Japanese, they are scarcely visible. In others, as the Hindu, Indian of the 
Andes, &c., they are numerous, large, and almost tubercular. In others, as the 
negro and King George Sound Australian, they are limited to two or three well- 
marked serrations. The form and proportions of what I shall call the thumb, 
are also different. In some, as the Mozambique Africander, Californian Indian, 
and Indian of the Andes, the thumb is excessively developed; in others, as the 
European, the Japanese, and Australian, only moderately so. The form of the 
penultimate joint also varies to a very considerable extent, in some being long, 
narrow, elongate and straight; while in others it is conical, curved, short, and 
broad at the base. . 
There remains the question, what is the value of these differences as bearing 
upon the unity of the human species? I am bound to confess that I think 
the question is left exactly where it was before. It has been proved that there 
are differences, and that these differences are constant and permanent—that is 
no doubt something. But, unluckily, these differences are most singularly 
similar to the differences in the races whose unity is the question in dispute, and 
to solve which this evidence has been adduced. If I cannot believe that the 
negro is a different species from the European, on account of his being black 
instead of white, neither should I believe that the Pediculus of the Negro: is 
different from that of the European because it is black instead of white. If I 

