HISTOLOGY OF THE LAND -PL AN AKI AN S OF CEYLON. 
131 
termination of the sheath of the pharynx. The muscular attachment of the pharynx to 
the roof of its sheath is confined to the region immediately surrounding the tube by 
which it leads into the digestive tract, and it is thus anterior to the middle of the organ, 
and forms a sort of pedicle. The oral aperture lies immediately over the centre of the 
pharynx. In Bhynchodemus the pharynx has the form of a cylinder directed antero- 
posteriorly, and narrowed in front and behind, and which may thus be said to be cask- 
shaped (“ doliiformis ,” Stimps.). The pharynx is perforated in the direction of its 
length by a tube which runs directly into the digestive tract, entering it by an aperture 
having the same relation to the sheath of the pharynx as in Bipalium. The pharynx is 
attached to its sheath only at its anterior extremity. The cylindrical form of pharynx 
is evidently the older and simpler one, and is that invariably possessed by the lower 
Rhabdoccele Planarians. The folded mouth of Bipalium is to be regarded as a modifi- 
cation of that of Bhynchodemus, the mouth of the cylinder having been gradually spread 
out until the whole organ became a flattened sucker, which, when retracted and packed 
away, assumes the form shown in the figure. Regarding this as being the case, and 
considering therefore the long irregular slit between the lips of the pharynx of Bipalium 
to be homologous with the rounded aperture at the extremity of the cylindrical pharynx 
of Bhynchodemus , the muscular arrangement in the two cases will be found to be 
identical. The pharynx is built up of an internal and an external set of longitudinal 
and circular muscular fibres, which muscular masses are connected by transverse fibres, 
in the interstices of which is a quantity of glandular matter. The outer muscular wall 
consists of external fibres, which run from the point of attachment of the pharynx 
towards the margin of its aperture or lips, and which must therefore be considered 
longitudinal. These longitudinal fibres, as will be seen from Plate XII. fig. 9, are 
extremely stout, and are succeeded inwardly by a zone of circular fibres, internally again 
to which are transverse or radiating fibres crossed by scattered circular fibres, and 
with stout longitudinal ones in their interstices. A wide zone, occupied by loosely 
packed radiating fibres, only intervenes between the outer muscular tissue of the 
pharynx and its inner longitudinal and circular muscles (Plate XII. fig. 8) ; and in this 
wide zone .is a considerable quantity of glandular tissue, which is more abundant in 
Bipalium than Bhynchodemus. The inner circular muscular coat which clothes the 
tubular cavity of' the pharynx immediately beneath its epithelium is composed of densely 
packed fibres, and stains, as do the corresponding inner circular tissues in the penis, 
vagina, &c., very deeply with carmine. The exterior of the pharynx and the walls of 
its sheath are lined with an epithelium, in which no definite cell-structure could be 
observed; but it appeared transparent and marked by vertical lines, which might 
represent separation into cellular elements. In the interior of the pharynx the epithe- 
lium is, especially towards the margin of the lips or aperture, composed of long pear- 
shaped elements, which were ascertained from chromic-acid preparations to be in 
Bipalium covered with cilia, and which are probably ciliated in Bhynchodemus also, 
although no ciliation was discernible in spirit preparations. 
