DISTOMUM HEPATICUM 3 



the generative opening, an orifice in the mid-ventral line. 

 Distornum is a hermaphrodite or monoecious animal, and the 

 male and female ducts open conjointly at the generative orifice. 

 At the extreme posterior end of the animal there is a small 

 pore by which the main canal of the excretory system opens 

 to the exterior, and on the dorsal surface there is a small 

 aperture in the middle line at about one-third of the length of 

 the animal from the anterior end : this is the opening of the 

 so-called Laurer-Stieda canal, of which the function is not 

 fully known. The whole surface of the body is covered with 

 small rod -like scales, which project backwards, and are 

 embedded in as many little pockets of the external layer or 

 cuticle. Their structure will be described further on. 



The mouth opens into a nearly globular muscular pharynx, 

 which is continued posteriorly into a short oesophagus. In 

 front of the ventral sucker the alimentary canal divides into 

 right and left branches, which run on either side of the middle 

 line to the posterior end of the body, and give off on their 

 outer borders a number of branched offsets or diverticula, 

 which extend right up to the margins of the body (fig. i, A). 

 There is no anus. 



The excretory system can only be seen clearly in specimens 

 which have been injected with some colouring matter through 

 the excretory pore. It consists of a main duct relatively of 

 considerable size, which runs forward in the middle line from 

 the excretory pore for about three-quarters of the length of 

 the animal, and then breaks up into three or four branches 

 (fig. i, C). Usually there are four such branches, a dorsal 

 and a ventral on each side, but the arrangement is not con- 

 stant. Throughout their courses the main duct and its 

 branches give off numerous side branches, which divide 

 repeatedly, their ramifications anastomosing freely with one 

 another, and forming a network which extends to every part 

 of the body. The ultimate ramifications are continued into 

 very fine tubules, with thin transparent walls, and these, 

 after a more or less convoluted course, end in little trans- 

 parent vesicles known as flame-cells. A flame-cell has thin 

 elastic walls, in which fibrillae crossing one another in several 

 directions may be traced. Internally the flame-cell and the 

 part of the canal nearest to it bears a few very long isolated 

 cilia, which are constantly in motion, and produce a flickering 



