1873,] Histology of the Land-Planarians of Ceylon. 171 



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, Ehynchodemus, and Geodesmus. The close 

 approximation of the intestinal diverticula in Bipcdium and Ehynchodemus, 

 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 Ehyncho- 

 demus and Bipcdium 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 Bipcdium and Ehynchodemus. A peculiar network of 

 connective tissue is characteristic of these vascular canals on section, and 

 is shown to present exactly similar features in Leptoplana tremellaris, 

 Dendrocoelum lacteum, and Bothriocephalus latus. The close agreement in 

 the relative position of the oviducts to the vascular canals in Dendrocoelum 

 and our land-Planarians is very remarkable. This primitive vascular 

 system is homologous with the body-cavity present in the embryo leech 

 and in Branchiohdella 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 he within the primitive vascular system, as do the corre- 

 sponding structures within the primitive body-cavity of the leech. 



Branches from the primitive vascular system in Bipalium serve to 

 erect the penis, and probably supply the glandular tissue with fluid for 

 secretion ; others possibly proceed to the ciliated sacs in the head, and 

 perform an excretory function. A small marine Planarian was found to 

 contain haemoglobin. In Bipalium there are a series of separate testes 

 disposed in pairs, as in the leech. In Ehynchodemus the testicular cavities 

 are more closely packed, and follow no such definite arrangement. The 

 ovaries are simple sacs in both Bipalium and Rhynchoclemus, and are 

 placed very far forwards in the head, a long distance from the uterus. 

 In Bipalium short branches given off from the posterior positions of the 

 oviduct are the rudiments of a ramified ovary, such as exists in Dendro- 

 coelum lacteum. There are also glands present, which probably represent 

 the yelk-glands and shell-making glands of aquatic Planarians in a more 

 or less rudimentary condition. There is a comparatively simple penis 

 and female receptive cavity in both Bipalium and Ehynchodemus. In 

 Bipcdium there is, further, a glandular cavity at the base of the penis 

 (prostate). The organs described as nervous ganglia by Blanchard in 

 Polyclaclus are almost certainly its testes and ovaries ; and therefore the 

 arrangement of these bodies in Polyclaclus is the same as that in 

 Bipcdium. 



