1881 .] 
223 
[Burgess. 
THE STRUCTURE OF THE MOUTH IN THE LARVA OF 
DYTISCUS. 
BY EDWARD BURGESS. 
As has long been known, the larva of Dytiscus, called in Eng- 
land the water-tiger, sucks the juices of its prey by means of a 
small canal which perforates its long sickle-shaped mandibles. 
No other opening into the head is evident, and authors are agreed 
in desciibing the creature as mouthless. Thus Westwood says, 
“ The mouth is remarkably constructed, being destitute of the 
ordinary aperture, so that the insect may be, and indeed has been, 
described as wanting a mouth ; ” 1 and again Lacordaire c alls the 
mouth “ completement close, se compose d’un menton . . . et 
de mandibules falciformes, aigues, sans dents, creuses et percees 
d’une petite ouverture pres de leur extremite.” 2 De Geer, as 
quoted by Westwood, 3 indeed “ suggested that the insect must be 
provided with some other means of taking food, as he observed 
one of the larvae not only suck the juices of an aquatic wood- 
louse, but also devour, by small degrees, all its solid parts.” No 
writer has, however, shown anatomically how the food passes from 
the mandibular, into the alimentary canal, or, except De Geer, 
even seen reason to guess the existence of an oral aperture until 
Meinert, a few years since in a short paper, 4 stated that he had 
forced the contents of the alimentary canal out from under the 
clypeus, as well as from the mandibular openings. Moreover he 
passed a hair into the mandible and saw it enter the head, through 
the basal mandibular opening, and I therefore presume he under- 
stood the modus operandi of sucking, as I shall state it below, 
although he gives no anatomical particulars, and did not see the 
mouth-lock. 
Passing now to the water-tiger itself, a cursory inspection will 
detect the oval opening on the inside of the mandibles near 
their tip (see the left mandible in figure 1) ; from this opening 
a canal leads along the inner surface to a basal opening on the 
4 Mod. Classif. of Insects. I, 100. 2 Coleopt6res I, 407. % Loc. cit. 
4 Om Mundens Bygning hos Larverne af Mynneleontiderne, Hemerobierne og Dy- 
tiscerne. Videnskab. Meddelelser fra Naturhist. Foren. Kjobenhavn, 1 879-8*0, I, p. 69. 
