HISTOLOGY OF THE L AND-PL AN AEIAN S OF CEYLON. 
133 
side, at the same level with them, and closely abutting on them. In Dendroccelum lacteum 
similar spaces, situate at equal distances from the median line of the body and towards 
its ventral surface, are to be seen in a transverse section of the animal’s body (Plate X. 
fig. 8, W, W). These spaces are, as in the Land-Planarians, little stained with carmine ; 
and the oviduct (OD) also has exactly the same relation to them. There can be no 
doubt as to the homology of these spaces with one another ; and, as will be seen further 
on, they are remarkably similar in their minute structure. The spaces (W, W) in I). 
lacteum are the main water-vascular trunks seen in section, and those of the Land- 
Planarians, as homologous with them, must receive the same appellation. The water- 
vascular trunks of Leptoplana tremellaris are found similarly situated and constructed 
on section (Plate XIV. fig. 1, W). Part of one of the drawings of Sommer and Landois’s 
paper on the sexually mature joints of Bothriocephalus latus has been reproduced in 
Plate XIV. fig. 2, in order to show the very close resemblance in structure between the 
lateral vessels of that worm and those of the Planarians. In Bipalium and Bhyncho - 
demus the pair of main vascular trunks extend throughout the entire length of the 
body, preserving their relative position to the ambulacral line and body-structures 
generally. In Bhynchodemus they terminate abruptly with rounded ends at both 
extremities of the body, as mayT>e seen, as far as the anterior extremity is concerned, in 
Plate XIV. fig. 5. In Bipalium, on the other hand, the vascular trunks, though ter- 
minating posteriorly as in Bhynchodemus , spread out in the anterior extremity in an 
irregularly ramified manner (Plate XIV. fig. 4), the ramifications being imperfectly 
defined by rows of vertical muscular fibres. The wide expansion of the vascular trunks 
in the head of Bipalium is seen in vertical section in Plate XIV. fig. 2. Frequent 
branches are given off from the vascular trunks in both Bhynchodemus and Bipalium ; 
and in some preparations they are conspicuous by their not being stained with carmine. 
These branches usually take a transverse course, and are in reality irregular lacunae, 
having no more definite wall than their main trunks. The large transverse trunks con- 
necting the main trunks in Bhynchodemus have already been spoken of : these are seen 
in longitudinal sections to be a series of irregular transverse channels hollowed out in 
the intervening muscular mass, and separated from one another by irregular intervals. 
Other finer transverse channels may be traced passing off from the vascular trunks 
(Plate XIII. fig. 15), being especially well seen in Bhynchodemus. As will be seen from 
Plate XIV. fig. 4, the large vascular space in the head of Bipalium does not extend to 
the verge of that structure, but is separated from this by a zone of solid tissue. 
Through this zone of tissue proceeds in straight lines a series of fine branches or tubular 
spaces, which are directed outwards to the margin of the head, and appear to pass 
directly to the peculiar ciliated sacs which there exist, and possibly to communicate 
through these with the exterior. These branches are figured, as seen in a longitudinal 
and horizontal section, Plate XV. fig. 3 ; and one may be sometimes traced passing 
from the lateral extremity of the vascular space to the papillary line in the vertical 
section, Plate XIV. fig. 3. The relation of these branches to the ciliated sacs will 
