NEW CESTODKS FROM THE TASMANIAN DEVIL. 687 



are of very large size, and it appeared to me that that on the pore 

 side of the segment was a little the larger of the two. This, then, 

 is the first important point about these vessels, ^. e. that there is 

 a very large ventral tube on each side of the body and a very 

 minute dorsal tube. In following out a series of transverse 

 sections, it is seen that the lumen of the large ventral water- 

 vessels is occasionally occluded by a delicate diaphragm-like 

 sheet of membrane which is abundantly nucleated. There is no 

 question of a narrowing of the calibre of the tube, but of an 

 actual membrane Avhich extends partly across it here and there. 



In sagittal sections the existence of these membranes stretch- 

 ing partly across the lumen of the water vascular tube is quite 

 obvious. They occur, moreover, on both sides of the body, that is 

 to say in the case of both ventral tubes. The reason for emphasizing 

 this fact will be apparent later. In the longitudinal sagittal 

 sections referred to it will be seen that there ai'e several of these 

 membranes which stretch a good way across the water-vessel, 

 and though two membranes arising from different sides of the 

 vessel do not actually meet, the edge of each stretches beyond the 

 edge of the other, so that the tube would appear, when viewed in 

 the direction of its length, to be entirely occluded. It is note- 

 worthy that these diaphragms, so to speak, arise indiffei'ently 

 from both sides. The exact arrangement will be j)lain from the 

 annexed drawing (text-fig. 99, p. 688). I have noticed that in some 

 of the posterior proglottids the lumen is actually occluded once 

 in each proglottid. The two ends' of two oppositely projecting 

 membranes are connected by a continuous though very thin 

 membrane which connects the thicker extremities of the lateral 

 projections. This median part appears to be nowhere deficient, 

 and the water vascular system is thus divided up in these regions 

 of the body into a series of chambers. 



I presume that these numerous membranes stretched across the 

 large vessels correspond to what has been figured in other tape- 

 worms as valves. I have emphasized the fact that they occur on 

 both sides of the body, because they carry on the pore side the 

 genital ducts which actually perforate their substance and lie in 

 their thickness. This perforation is limited to the larger of these 

 valve-like structures which arise from the outer side, and it has 

 been produced I imagine by the extension round the ducts of the 

 water-vessel, which is of much greater diameter in the posterior 

 than in the most anterior segments. In the case of these latter, 

 as already mentioned, the generative ducts pass to one side of the 

 water-tube. 



Another important feature in the water vascular system of this 

 tapeworm is the total absence of transverse vessels uniting the 

 longitudinal trunks in such segments. This state of afiairs is 

 not unknown among other Cestoidea — it occurs, for example, in 

 llymenolejns acuta * — but it is not common. Nor is this lack of 



* V. Janiclii, Zool. Anz. Bd. xxvii. 1904, p. 776. 



