220 Prof. J. C. Schjodte on Phthiriasis, and 
that is, Erichson and Simon’s so-called “ palpi ;”” but, not to men- 
tion that the two rows will never appear quite alike, there are two 
points here to observe :—first, that these “ palpi,” when they ap- 
pear, always show themselves further back than the hooks; and 
secondly, that we never succeed in seeing hooks and “ palpi” at 
the same time and in the same preparation: on the contrary, 
when the hooks appear, the “palpi” are gone, and vice versd. 
There is now no room for wonder that Erichson and Simon found 
no hooks, but only “ palpi,” whilst Landois saw “ palpi” but no 
hooks ; at the same time the uncertainty remains as to what 
these small organs really are. As for the so-called mandibles, 
they always remain the same, just as represented by our three 
authors. 
Let us for a moment content ourselves with this figure, and 
seek the guidance of our authors in explaining it. But here we 
at once meet with a certain degree of vacillation. In his first 
statement Erichson does not seem quite inclined to acknowledge 
the haustellum, which he alludes to as the “ so-called” haustel- 
lum. But he must have overcome his doubts in this respect 
when he had repeated his investigation together with Dr. Simon; 
for then he spoke quite unreservedly of an haustellum provided 
with palpi. Landois, too, describes the elongated dark object 
as an haustellum, but at the same time considers it equivalent 
to a bifid labrum. it is true that his expression is that he 
“first ” (zuerst) found a labrum on the haustellum; but, as he 
does not mention any further or second particular, he seems to 
have really considered that the haustellum was entirely formed 
by the labrum, though, strictly speaking, he only says that the 
labrum forms the upper part (Decke) of it. But beyond this 
our authors furnish us with no details of this haustellum, from 
which we may safely conclude that they have not observed any- 
thing beyond the same confused image presented by our pre- 
paration. 
Here, then, according to these authors, we have a mouth 
composed of the following parts :—(1) an haustellum—according 
to Erichson and Simon, provided with a pair of four-jointed 
palpi, but according to Landois exhibiting a bifid labrum 
armed with hooks at one extremity and reaching with the other 
far back into the head; (2) a pair of mandibles wnderneath 
the haustellum. Hvidently this combination is fundamentally 
different from the mouth of any other known type of Arthro- 
pods; and as it always is a matter of hesitation to acknowledge 
as well founded morphological statements destroying a hitherto 
supposed harmony in the multifarious forms of nature, it might 
naturally have been expected, at least of Erichson, that he 
would enter more fully into the matter in this respect. How- 
