134 
ME. H. N. MOSELEY ON THE ANATOMY AND 
be more carefully considered when these latter organs are treated under the head of 
special sense-organs. The structure of the spongy tissue with which the water-vascular 
spaces are filled is very remarkable. In Bothriocephalus latus, as in Leptoplana , 
Dendrocoelum, Bipalium, and Bhynchodemus , it is characterized by being very little 
stained with carmine (Sommer and Landois, loc. cit. p. 13). The tissue forms a fine 
reticulation, in which are pierced oval or rounded openings. A comparison of 
figs. 1, 2, & 7, Plate XIV., will show the remarkable resemblance of structure in the 
various worms. In Bipalium and Bliynchodemus the main water-vascular trunks are 
traversed by muscular fibres of the body-mass, which give a characteristic appearance to 
these structures, from the circumstance that they form two parallel sets, which preserve 
a constant direction throughout the body and cross one another at a constant angle. 
One set is nearly vertical in Bipalium Ceres (Plate X. fig. 6), slightly inclined inwards 
(i. e. towards the middle line) interiorly in B. Diana (Plate X. fig. 5), and inclined rather 
outwards in Bhynchodemus Thwaitesii. The other set has about the same inclination 
in all these species, and will be seen to slope downwards and outwards on each side at 
an angle of about 60° with the vertical. The two sets of fibres thus crossing include 
between each other rhomboidal spaces. The fibres are here said to be muscular, because 
they are continuous with undoubted muscular fibres of the body-mass ; but, as will be seen 
in Plate XIV. fig. 6 (where a portion of one of the main vascular trunks of Bipalium 
Diana is shown greatly magnified), these fibres give off ramifications which are histolo- 
gically continuous with the fine connective-tissue network occupying their interspaces, 
and this, again, in direct connexion with the peculiar protoplasmic elements (X, X) which 
have been before treated of. 
I observed no cilia within the .vascular canals of any of the Planarians which I 
examined. 
The term “ water-vascular system ” has here been given to the peculiar canals or spaces 
in Bipalium and Bhynchodemus, because they are most evidently of the same nature as 
the lateral vessels of Taenia and Bothriocephalus, to which that name was given by 
V. Siebold, and because they are distinctly homologous with the longitudinal canals of 
Dendrocoelum and Leptoplana, which usually receive that appellation. But the term 
would seem to be rather unfortunate, because a “ water-vascular system ” has come to 
be regarded more or less as necessarily an excretory organ (“ Excretions-Organ,”.KEFER- 
stein, loc. cit.), and to have necessarily some communication with the exterior. The 
term “ primitive vascular system” would seem to be more appropriate; for the case 
would seem to be as follows. In primitive animal forms of more or less homogeneous 
constitution, as advancement in organization proceeds, a circulation of the body-fluids 
becomes a necessity, and vascular spaces become gradually developed in certain parts 
and along certain lines of the' body-mass. These spaces become more and more clearly 
defined, and assume at length the form described as existing in Bipalium, where the 
spaces or canals are by no means .as yet open channels, but merely tracts where the body- 
tissue has become extremely porous and permeable to fluids, and which are still traversed 
