ON A NEW REPTILIAN CESTODE. 107 



vessels pass down along each side well within the medulla. 

 Both have a round lumen, that of the ventral stem being 

 much greater than the other, and possessing a very well 

 defined margin. The dorsal vessel is quite small in section 

 and is not always readily recognisable whilst the other is. 

 Its position is above and generally slightly inwards from 

 the ventral stem which is situated practically in the middle 

 of the lateral region of the medulla and just internally 

 from the nerve. The two tubes lie close together except 

 in the region of the cirrus sac where they widely diverge, 

 the genital ducts passing between them. The transverse 

 vessels have a lumen as great as that of the ventral vessels. 

 In the younger part of the chain, the excretory canals have 

 a sinuous course (figs. 2, 4). 



The rudiments of the genital apparatus appear early as 

 a deeply staining cord of cells situated transversely to the 

 length of the strobila. From this cord the vas deferens, 

 cirrus sac and vagina soon become differentiated, and a 

 little further back the last named may be traced posteriorly 

 to the developing female genital complex. The most con- 

 spicuous part of this complex represents the receptaculum 

 seminis, the ovary being small and very slightly branched 

 as it does not become nearly as deeply stained as the vitel- 

 larium it may easily be overlooked (fig. 2). 



By this time the testes have appeared though they are 

 few. They now increase in number and size and are 

 arranged in a layer situated in the dorsal region of the 

 medulla. Their form is spheroidal and their average size 

 in sexually mature segments is about twenty-two micra 

 long by thirteen broad. In transverse sections, they are 

 seen to occupy about two-thirds of the dorso-ventral 

 diameter of the medulla. The number increases from 

 about thirty in young segments to about ninety in those 

 which are mature. The vesicles are disposed laterally and 



