Trematode from Protopterus. 91 



backwards for about a third of the length of the body. They 

 are situated almost entirely externally to the gut-branch on 

 either side. The two vitelline ducts cross the body just 

 behind the ovary, on the dorsal side, forming a straight line 

 with one another. Owing to the obscurity caused by the 

 excessive development of the uterus at this level, the precise 

 relationships of the complex of organs and ducts belonging 

 to the female apparatus have not been worked out, and the 

 presence of Laurer's canal remains uncertain. 



The uterus is very well developed and voluminous in most 

 of the specimens. Passing backwards from its origin behind 

 the ventral sucker, it forms a double sinuous loop in the 

 hinder end of the body. It then turns forward and runs, 

 still with a very sinuous course, up the middle of the body. 

 In this region it becomes much swollen, giving the animal a 

 very prominent contour on the ventral side, and is densely 

 packed with eggs. Finally, it opens into a thick-walled 

 vagina, which begins at the level of the hinder edge of the 

 ventral sucker, and runs forward with a curve almost parallel 

 to the cirrus-sac, with which it is about equal in length. The 

 vagina has a strong coat of circular muscles. The fully formed 

 eggs contained in the uterus are oval, and have a moderately 

 thick brownish shell, with a distinct cap at one end, which 

 is easily separated by slight pressure on the cover-glass. 

 The eggs measure 0*04 mm. in length and 0*02 mm. in 

 breadth. In a very young specimen, in which there were as 

 yet few eggs in the uterus, they were found to have precisely 

 the same dimensions as in the mature individuals. 



Excretory Organs. — The excretory system presents in this 

 species an apparently unique condition. The presence of a 

 very large and peculiar sac, with a comparatively enormous 

 aperture, on the dorsal side, has already been mentioned. 

 This sac appears to be lined with a special epithelium, con- 

 sisting of a single layer of rather tall cells. Unfortunately, 

 owing to the poor fixation of the material, I am unable to 

 describe the nature of this epithelium more precisely, or to 

 decide whether it is ciliated or not. At all events, it is clear 

 that the sac is not merely lined with a continuation of the 

 external cuticle of the animal. The cavity of the sac is 

 usually filled with a mass of loose matter, which may be a 

 product of excretion or may be of mucous nature. 



At its anterior end the sac gives off a small ventral diver- 

 ticulum, into which, apparently (though not directly), the two 

 main collecting vessels of the excretory system empty their 

 contents. I have experienced great difficulty in seeing clearly 

 the termination of both of these tubes in the same preparation 



