Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Todd, Robert Bentley
among naturalists*; but since a certain oral 
appendage, at least in some of the orders, 
has received by common consent the name 
of lingua, I shall briefly describe it. The 
mouth of insects is furnished with two lips 
— an upper lip, or labrum, and a lower lip 
or labium ; besides four jaws — a mandible,’ 
or upper, and a maxilla, or lower jaw, on each 
side. The labium, or lower lip, is divisible 
into two parts — a mentum, or basal joint, 
and a more flexible piece moving on this, the 
ligula, or labium proper. On the inner sur¬ 
face of this labium is developed a small pro¬ 
cess having a certain resemblance to a tongue, 
situated in front of the oesophageal orifice, 
and generally anchylosed with the labium at 
the front and sides of that opening ; in some 
cases, however, as in the locusts and dragon¬ 
flies, it is free. This process Cuvier con¬ 
sidered merely as a part of the labium, and 
accordingly called it labium; Fabricius and 
Latreille gave it the name of ligula. In shape 
it is generally short, but in bees it is long ; it 
is frequently simple, but in the wasp its apex 
is trifid, the same in Melolontha stigma; in 
Canobus it possesses three short teeth ; in 
Elaphras it terminates in a single tooth or 
point. In substance it generally approaches 
to a cartilaginous consistence, but in the Ortho- 
ptera and Libellulæ it is much more fleshy : 
and in the predaceous beetles it is as hard 
and horny as the integument. In some cases 
it is immovable, in others projectile and re¬ 
tractile within the mouth ; in some cases 
smooth, in others covered with hairs, as is 
the case in the common hive-bee ; in Melo¬ 
lontha stigma the hairs are incurved- In the 
hive-bee the upper part of the tongue is car¬ 
tilaginous, and remarkable for a number of 
transverse rings : below the middle it consists 
of a membrane longitudinally folded in in¬ 
action, but capable of being inflated to a con¬ 
siderable size : this membranous bag receives 
the honey which the tongue, as it were, laps 
from the flowers, and conveys it to the 
Mollusca.—Gasteropoda. In the acephalous 
mollusca there is, of course, no tongue. But 
the Gasteropoda are provided with a very sin¬ 
gular apparatus, which, since it is usually called 
the tongue, cannot be allowed to pass obser¬ 
vation here, though its right to such an ap¬ 
pellation is somewhat questionable. Its form 
is subject to much variation, but it may be 
described generally as a thin membrane, long 
and narrow, the greater extent of which is 
rolled into a tube. This tubular part (Jig. 759. 
A, b), occupies the posterior portion of the 
membrane, the end being closed, while its an¬ 
terior extremity is open and in connection 
with the oesophagus ; in front of the tubular 
part of the tongue is a continuation of the 
same membrane, which is here flat, and in many 
* Ce qu’on a nommé langue dans les coléoptères 
et les orthoptères, ou l’extremité membraneuse de la 
lèvre inférieure, en mérite à peine le nom. Cuv., 
Leçons d’Anat. Comp., t. iii. p. 347. 
f Kirby and Spence, vol. iii. p. 453. 
species also, as in the common whelk (Buc¬ 
cinum undatum), it is recurved (fig. 759. A, 2). 
Fig. 759. 
5 A. 1. Vertical section of bead of Limax maximus, 
showing the relative position of the mouth, a; 
tongue, b ; and oesophagus, c. 
2. Retracted proboscis of Buccinum undatum, a, 
mouth; b, tongue; c, oesophagus. 
B, single row of tongue-teeth of B. undatum. 
This membrane is covered on its upper sur¬ 
face with transverse rows of minute teeth, or 
rather plates with tubercular or toothlike pro¬ 
cesses upon them. The number of rows is 
considerable, and very variable, the terrestrial 
species averaging, probably, about eighty, and 
the marine possessing often many more ; the 
number of plates in each row is subject to 
still greater variation : the common whelk 
(Buccinum undatum) has but three (fig. 759. 
B), the large garden slug (Limax maximus) 
has 180. The shape of the plates in terres¬ 
trial gasteropoda is usually irregularly qua¬ 
drangular, slightly longer than broad, while in 
some fluviatile and marine species they as¬ 
sume most complicated and elegant forms 
(fig. 759. B). The centre plate of the row is 
always symmetrical, and its denticular projec¬ 
tions point in the direction of the closed end, 
i. e. backwards, and nearly horizontally. The 
plates on either side of this central plate usu¬ 
ally assume in terrestrial gasteropods much 
the same form and direction, while some of 
the fluviatile and most of the marine species 
present such an endless variety of forms, that 
the most that can be said of them, generally, 
is that the dental processes point backwards. 
Fig. 759. B represents a row of the denti¬ 
gerous tongue-plates of the Buccinum unda¬ 
tum : there are seen to be only three ; the cen¬ 
tral one symmetrical, the lateral ones of very 
different form, individually non-symmetrical, 
but having an exact correspondence to one 
another. The tongue itself (fig. 759. A, 2) is 
attached, as before stated, to the oesophagus 
near its anterior extremity, and lies beneath 
it. In the Helices and Limaces it is enveloped 
in the muscular head of the gasteropod (fig. 
759. A. 1), its posterior blind end being just 
visible at the back part of the head, some dis¬ 
tance below the point where the oesophagus 
leaves that part and passes into the abdominal 
cavity. In the whelk tribe it lies beneath, and 
parallel to, the oesophagus, and is free, though 
surrounded by strong muscular bands, the 
general direction of which is also parallel to 
the tongue. It is in this tribe that the an¬ 
terior end of the tongue is curved downward,


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