on the Structure of the Mouth in Pediculus. 221 
ever, neither he nor any of the other authors have said one word 
on this highly important part of the question. 
Thus left to our own resources, let us once more look at our 
preparation. The haustellum apparently giving uo immediate 
clue to a proper interpretation of what we observe, let us con- 
centrate our attention on the so-called mandibles; and if in so 
doing we have the benefit of some knowledge of the general 
morphology of Arthropods, a number of considerations will 
soon present themselves which will gradually weaken the inter- 
pretation of these parts as mandibles, and at last prove altogether 
conclusive against it. For if we consider their diminutive size 
(their length in P. vestimenti, the largest of the species living on 
pe ite body, and the See ose of phthiriasis, is only 
=) to. — millim: Ey a breadth of =; to =; millim., and a thick- 
ness ic =i, to +4, millim.)—their as which is that of a 
narrow band equally broad at both ends complete want 
of teeth, articular processes, and muscles, of which no vestige is 
discernible—we must aver that such organs cannot possibly be 
mandibles. Nor can we stop here: mandibles cannot be stuck 
on arbitrarily any more than any other organ; they must have 
their place in the plan of the organism, and harmonize with all 
its parts. A glance at the structure of the Mallophagi, which 
offer themselves most naturally for comparison, will show at 
once what is required for an insect having mandibles; and yet 
Mallophagi feed only on the youngest and softest sprouts of 
feathers and hair, whilst Lice are accused of eating their way 
through such a covering as the human epidermis. Not only would 
the equipment of tendons and muscles be required, which these 
so-called mandibles in reality lack, but, besides this, space would 
be needed inside the head for the muscles, and also a surface on 
which their fixed ends could find support ; that is to say, the head 
would of necessity have to be broad, with a firm framework, 
which, again, would demand an entirely different structure of 
the thorax, limbs, &e. In short, if Lice had mandibles, they 
could not possibly be such soft creatures as they are, with a 
pointed head, strong climbing legs, and slow motion. 
Nor do these conclusions, which, in my opimion, are incon- 
testable, even yet exhaust the catalogue of improbabilities attach- 
ing to the theory of Lice being provided with organs for biting. 
For even those who advance this theory do not express any doubt 
that Lice live exclusively on blood, which they suck by means 
of an haustellum ; but why, then, should they take the trouble of 
biting or enawing holes in the epidermis by means of the mandi- 
bles, seeing that there is such a multitude of natural small 
openings in the human skin, that the haustellum, when inserted 
through one of these, at any rate nced perforate only a part of 
