312 lioyal Society: — 



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, 

 RhyncJiodemus, and Oeodesmus. The close approximation of the 

 intestinal diverticula in Bipalium and Rhynchodemus, and the 

 reduction of the intervening tissue to a mere membranous 

 septum is very striking, and seems to foreshadow the con- 

 dition of things in Annelids. The great difference in the form 

 of the mouth in Rhyiicliodemus and Blpalium 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 Rhynchodemus. 

 A peculiar network of connective tissue is characteristic of these 

 vascular canals on section, and is shown to present exactly similar 

 features in Leptoplana tremeUaris, Dendroccelum lacteum, and Bothrio- 

 cepluxlus latus. The close agreement in the relative position of 

 the oviducts to the vascular canals in Dendroccdum and our land- 

 Plauarians is very remarkable. This primitive vascular system 

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

 and in Branchiobdella 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 structures within the primitive 

 body-caAdty 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 haDmoglobin. In Bijxdium there 

 are a series of separate testes disposed in pairs, as in the leech. 

 In Rhynchodemus the testicular cavities are more closely packed, 

 and follow no such definite arrangement. The ovaries are simple 

 sacs in both Bipalium and Rhynchodemus, and are placed very 

 far forward in the head, a long distance from the uterus. In 

 Bipalium short branches given off from the posterior portions of 

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

 in Dendroccelum 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 Rhynchodemus. In Bipcdium, there is, further, 

 a glandular cavit_y at the base of the penis (prostate). The organs 

 described as nervous ganglia by Blanchard in Polycladus are 

 almost certainly its testes and ovaries ; and therefore the arrange- 

 ment of these bodies in Polycladus is the same as that in 

 Bipalium. 



The chain of nervous ganglia described as existing in Bipalium 

 {^phyrocephalus) by Schmarda, and which has been referred to 



