HISTOLOG-Y OF THE LAND-PLAN ASIANS OF CEYLON. 
14T 
and the longitudinal internal, in Turbellarians the reverse is the case. A wide gulf is 
thus apparently placed between these groups. In Bipalium there is an external circular 
muscular coat, which even presents the same imbricate structure which is found in it in 
leeches and other worms. In Dendroccelum lacteum there is also an external circular 
coat. In cases where a distinct external circular muscular coat is absent, it is repre- 
sented by a thick membrane, which is very probably contractile. The question resolves 
itself simply into a more or less perfect fibrillar differentiation of that membrane. All 
Turbellarians are built on the same essential type, as regards muscular arrangement, 
as are other worms. The general muscular arrangements in the bodies of Bipalium 
and Bhynchodemus have become much modified from those of flat Planarians by the 
pinching together and condensation of the body ; but they are nevertheless referable to 
the same type. 
The digestive tract consists of three tubes (one anterior, two posterior), as in other 
Planarians, and as in the embryo leech before the formation of the anus. Characteristic 
of Land-Planarians, and consequent on the condensation of the body, is the absence of 
all diverticula from the inner aspects of the two posterior digestive tubes. This is 
found to be the case in Geoplana, Bipalium , Bhynchodemus, and Geodesmus. The 
close approximation of the intestinal diverticula in Bipalium and Bhynchodemus, and 
the reduction of the intervening tissue to a mere membranous septum, is very striking, 
and seems to foreshadow the condition of things in Annelids. The great difference in 
the form of the mouth in Bhynchodemus and Bipalium is also remarkable, considering 
the many points in which these forms are closely allied. 
A pair of large water-vascular trunks, or, as they are here termed, primitive vascular 
trunks, are conspicuous objects in transverse sections of the bodies of Bipalium and 
Bhynchodemus. A peculiar network of connective tissue is characteristic of these vas- 
cular canals on section, and is shown to present exactly similar features in Leptoplana 
tremellaris , Dendroccelum lacteum, and Bothriocephalus latus. The close agreement in 
the relative position of the oviducts to the vascular canals in Dendroccelum and our 
Land-Planarians is very remarkable. This primitive vascular system is homologous 
with the body-cavity present in the embryo leech and in Branchioib della throughout 
life. It is not necessarily an excretory system, though the term water-vascular system 
has been generally considered to imply such a function for it. The nerves and ganglia 
of Planarians lie within the primitive vascular system, as do the corresponding struc- 
tures within the primitive body-cavity of the leech. 
Branches from the primitive vascular system in Bipalium possibly proceed to 
the ciliated sacs in the head, and perform an excretory function. A small marine 
Planarian was found to contain hemoglobin. In Bipalium there are a series of separate 
testes disposed in pairs as in the leech. In Bhynchodemus the testicular cavities are 
more closely packed, and follow no such definite arrangement. The ovaries are simple 
sacs in both Bipalium and Bhynchodemus, and are placed very far forwards in the head, 
a long distance from the uterus. In Bipalium short branches given off from the 
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