228 Prof. J. C. Schjédte on Phthiriasis, and 
in the same manner are transformed into a tube ending im four 
small lobes placed crosswise. It follows that when the whole 
instrument is exserted, we perceive a long membranaceous flexible 
tube hanging down from the labium, and along the walls of this 
tube the setiform mandibles and maxille, in the shape of long 
narrow bands of chitine. In this way the tube of suction can be 
made longer or shorter as required, and easily adjusted to the 
thickness of the skin in the particular place where the animal is 
sucking, whereby access to the capillary system is secured at any 
part of the body. It is apparent, from the whole structure of 
the instrument, that it is by no means calculated on being used 
as a sting, but is rather to be compared to a delicate elastic probe, 
in the use of which the terminal lobes probably serve as feelers. 
As soon as the capillary system is reached the blood will at once 
ascend into the narrow tube, after which the current is contmued 
with increasing rapidity by means of the pulsation of the pumping- 
ventricle and the powerful peristaltic movement of the digestive 
tube. 
We can now easily explain what it is that Erichson, Simon, 
and Landois have mistaken for mandibles and palpi. When the 
labium is pressed down against the chitinous band above men- 
tioned, it touches and covers precisely the thinnest middle part 
of it, whilst the firmer lateral parts of the band by the pressure 
become further removed from each other, or even entirely sepa- 
rated if the pressure is increased, and thus they assume the ap- 
pearance which led to their being misinterpreted as mandibles. 
It is furthermore evident that the barbs of the labium must 
assume many different positions, according to whether the elastic 
part on which they are fixed is more or less protruding from or 
retracted into the head, or more or less unfolded or contracted 
in itself. When the labium only just peeps out of the head, a 
greater or smaller number of hooks may become visible in front 
of it, and then we have the image represented on Dr. Landois’s 
figure of the mouth in Phthirius inguinalis. But if the elastic 
part of the labium be folded up and entirely retracted in the 
head, the hooks will show themselves, by pressure and transmitted 
light, generally forming an irregular heap, but sometimes more 
regularly grouped, and even placed in an oblique line on one or 
the other side of the middle field, though never quite symmetri- 
cally on both. It is such an accidental lmear arrangement of 
the hooks that has been interpreted by Erichson and Simon as 
alpi. 
i How easily one may get upon a wrong scent by neglecting the 
study of the living animal, we can also learn from the statements 
of Burmeister, though he has come much nearer to the real 
truth. He founded his conclusions merely on dissection of the 
