DESCRIPTIONS OF FOUR DISTOMES. 29 



is situated about at the beginning of the second third of the body and has a length 

 of 0.4 millimetre and a width of 0.36 millimetre. The genital pore is on the ventral 

 surface near the posterior end of the pharynx, a little to the left of the median line. 

 The excretory pore is at the posterior end of the body. 



The digestive tract is made up of the pharynx, the oesophagus, and the intes- 

 tinal caeca. The pharynx has a length of 0.06 millimetre. A very short oesophagus 

 with a length of 0.02 millimetre follows. The intestinal caeca are simple tubes with- 

 out lateral projections and have an average width of 0.04 millimetre. They are 

 longer than in R. ellipticus, extending beyond the testes; the right caecum is some- 

 what longer than the left one. 



The excretory vesicle is very long and voluminous. It has the shape of the 

 letter Y, the median portion extending forward as far as the ovary, and the crura 

 almost reach the branching of the digestive tract. The median portion is not only 

 of great length, but also of great width and depth. Posteriorly to the testes it occu- 

 pies at least half of the space within the body-wall. Near the ends of the intestine, 

 for instance, it has a width of 0.41 millimetre and a depth (dorso-ventral) of 0.13 

 millimetre (PL IV, Fig. 4), while at the posterior end of the uterine loop it measures 

 0.20 millimetre by 0.05 millimetre. At the hinder end of the animal the excretory 

 vesicle occupies practically the entire space within the body-walls. Between the 

 testes this vesicle is contracted to a fraction of its width behind those organs, but 

 immediately anterior to them it again expands so that it measures 0.41 millimetre 

 by 0.2 millimetre, the body of the worm itself at this region having a width of 0.66 

 millimetre and a thickness of 0.29 millimetre. Just behind the ovary the excretory 

 vesicle branches, and each branch has a width of about 0.13 millimetre and a depth 

 of 0.2 millimetre. The branches gradually become smaller toward the anterior end 

 of the animal, where they run alongside the cirrus-sac, to terminate a short distance 

 in front of the acetabulum. Throughout its entire course the excretory vesicle is 

 dorsal in position. 



The testes are two elongate, slightly lobate bodies situated side by side near 

 the centre of the body. The right testis is slightly in advance of the left one. They 

 measure about 0.32 millimetre in length, 0.16 millimetre in width, and 0.24 millimetre 

 in thickness, lacking but little of being as thick as the body itself. The vasa efferentia 

 pass from their anterior ends forward to a position dorsal to the posterior edge of the 

 acetabulum, where they unite to form the vesicula seminalis. This organ together 

 with a long pars prostatica and a short cirrus is enclosed in the large cirrus-sac, the 

 length of which is 0.7 millimetre and the width 0.16 millimetre. The vesicula semi- 

 nalis bends on itself in the posterior portion of the cirrus-sac. The pars prostatica 



