on the Structure of the Mouth in Pediculus. 215 
But his observations have been not less defective than those of Swam- 
merdam. ‘The hooks on the so-called haustellum do not exist at all, 
but there are instead a pair of strong four-jointed palpi ; the lice also 
possess very distinct mandibles, so that I cannot but entirely side 
with the unlearned, who maintain that the lice dite, in opposition to 
the opinion of the learned,—and that so much the more as the strue- 
ture of their mouth renders it impossible for lice to sting. It follows 
of necessity from these indications, that it becomes altogether im- 
possible to class Pediculini with Hemiptera as proposed by Nitzsch, 
a classification which Burmeister considered necessary on purely 
philosophical grounds.”’ 
In vain did Burmeister afterwards give a detailed account 
(Linnea Entomol. 1. 1857, p. 569, pl. 1) of the struc- 
ture of the mouth im Pediculus urius, agreeing with Nitzsch’s 
statements, and confirming the hypothesis of this author in his 
well-known treatise in Germar’s Magazine (“die Familien und 
Gattungen der Thierinsecten”’), vol. in. p. 804, viz. that the 
inner tube of suction consists of several sete. It was of no 
avail, as indeed it never does avail in science, simply to put 
forth one view as true and reject the opposite as false, because 
the one thing necessary for a final decision is to test the har- 
mony of the discoveries with the rational connexion of things : 
it is, so far, of small importance that Burmeister’s account 
contains several mistakes and faults. Accordingly we read, in 
Simon’s elaborate work on cutaneous diseases, published in the 
following year :— 
‘Concerning the structure of the mouth in lice, the earlier obser- 
vers supposed that they possessed an haustellum armed with hooks, 
which, however, as early as 1839, was denied by Erichson, who, on 
the contrary, discovered distinct mandibles, and a pair of four-jointed 
alpi. 
t wae the view formerly held is still favoured by many, I have not 
thought it superfluous to enter more fully on this matter. I have 
therefore, together with Professor Erichson, examined Pediculus 
capitis in this respect [Professor Erichson’s former investigations 
had been made on P. vestimenti|; and we found, by application of a 
strong magnitying-power, that the parts of the mouth were precisely 
as indicated by Erichson, and as drawn by me on tab. 7. figs. 4 & 5, 
In the head, under the haustellum (a), there are a pair of mandibles, 
of a brownish colour (4), and on the haustellum itself a pair of four- 
jointed palpi (ec). We have not examined the mouth in PAthirius. 
As long as it was believed that lice were furnished merely with 
an haustellum, it was supposed that they perforated the skin with 
this. "The existence of mandibles having now, however, been demon- 
strated, it must be assumed that they first bite through the skin 
with these, and then introduce the haustellum through the wounds 
thus produced. The palpi probably serve to discover the places 
