226 Prof. J. C. Schjédte on Phthiriasis, and 
I have hitherto conducted this investigation as slowly and as 
cautiously as I thought necessary in a matter so difficult, com- 
plicated, and so disputed ; but I think we have now arrived at 
a point from which we may without danger hasten more resolutely 
to the conclusion. In order to render my account as clear and 
perspicuous as possible, I shall m the sequel apply to all the 
different parts of the mouth those names which, from a morpholo- 
gical point of view, belong to them, forming as they do, in my 
opinion, a somewhat modified but nevertheless unmistakeable 
and complete mouth of the Khynchote type. 
Lice are no doubt to be regarded as Bugs* simplified in 
structure and lowered in animal life in accordance with their 
mode of living as parasites, small, flattened, apterous, myopic, 
crawling and climbing, with a conical head, moulded as it were to 
suit the rugosities of the surface they inhabit, provided with a 
soft, transversely furrowed skin, probably endowed with an 
acute sense of feeling, which can guide them in that twilight in 
which their mode of life places them. The peculiar attenuation 
of the head in front of the antennz at once suggests to the prac- 
tised eye the existence of a mouth adapted for suction. This 
mouth differs from that of Rhynchota generally in the circum- 
stance that the labium is capable of being retracted into the upper 
part of the head, which therefore presents a little fold which is 
extended when the labium is protruded. In order to strengthen 
this part, a flat band of chitine is placed on the under surface, 
just as the shoemaker puts asmall piece of gutta-percha into the 
back of an india-rubber shoe; as, however, the chitine is not 
very elastic, this band is rather thinner in the middle, in order 
that it may bend and fold a little when the skin is not extended 
by the lower lip. The latter consists, as usual, of two hard lateral 
pieces, of which the fore ends are united by a membrane so that 
they form a tube, of which the interior covering is a continuation 
of the elastic membrane in the top of the head ; inside its orifice 
there is a number of small hooks, which assume different po- 
sitions according to the degree of protrusion: if this is at its 
highest point the orifice is turned inside out, like a collar, where- 
by the small hooks are directed backwards, so that they can serve 
as barbs. These are the movements which the animal ex- 
ecutes after having first inserted the labium through a sweat-pore. 
When the hooks have got a firm hold, the first pair of sete (the 
* Many naturalists, although free from the error that the so-called ha- 
bitus, without any further examination of its character and origin in every 
case, is of any weight in such systematic questions as the one before us, 
nevertheless hesitate when it seems to be left quite out of sight. I may 
remind such of Aradus and similar genera, in order to show that not even 
is habitus violated by ranking Pediculini amongst Bugs. 
