190 
LABIAL PALPS. 
M i 
Fui. 370. — Mouth of 
as/>t'rsa X {. shoNving the lateral 
lobes or Ups and upper jaw (after 
Howes). 
tlie special mucous secretions from the unicellular glands of the organ 
of Semper; they represent the largely developed bilobed velum of 
larval life and are retaineil in the Limmvida’ in full proportions by 
the adult, hut have lost the marginal fringe of relatively very long 
cilia and also the locomotor function. 
Some authors distinguish three circum-oral lobes in the Gastropods, 
an upper lip which is somewhat rounded 
and often hears a number of pai)ill;e, and 
two lateral ones, which however are usually 
regarded as representing a cleft lower lip. 
'I'liese processes are not retractile like 
the ommatophores and are chiefly found in 
the predacious si)ecies,l)nt are also largely developed in the Llmna’ida\ 
furniing a considerahle circum-oral e.xpansion or enlargement, but in 
a less pronounceil form these labial lobes are jn’esent in other 
])ulmonates. In Liiixt.r, virion, etc., the upper li]) bears a number of 
distinct and rounded tubercles or ])a])illa‘, into winch the glands of 
Semper’s organ debouch (see j). liSo, f .'i.'iT), and which are innervated 
bv a liranch from each of the 
anterior tentacular nerves, which 
gives off to each ]iapilla of its side 
a nervous branch upon whii'b a 
small ganglion is developed. 
The laliial palj)s are, however, 
a more es])ecial feature of the 
I’elecypods. 'I'hey consist of two 
])airs of triangnlarly-oval, thin and 
biglily vascular processes, inner- 
vated by tlie cerebro-])leural ganglia 
and covered with richly ciliated o])itheliuni. 'fhey are formed by the 
excessive prolongation and out-growth of the anterior and ])Osterior 
margins of the oral ai)erture and hang 
down within the mantle cavity, enclosing 
between them a ciliateil groove conducting 
directly to the mouth the particles of food 
brought within the influence of the 
currents which the action of the cilia 
perpetually excite, and are therefore more especially alimentary and 
respiratoiy in function rather than of a tactile oi’ sensory character, 
Kui. 371. — .\nterior region of Anodonia 
cygnca, showing the position of the mouth 
and the relative disposition of the labial lobes 
and foot (after Moiiuin-Tandon). 
a.p. right anterior palp ; f. foot ; /./. right 
posterior jtalp ; ni. mouth. 
Fig. 372. — Anterior and posterior 
labial palps from the right side of 
Anodonia cygnca, isolated, X 3 
(after Moquin-Tandon). 
