332 ON SOME TKEMATODE PARASITES OF AUSTRALIAN FROGS 



aperture is in the middle line on the ventral surface, midway 

 between the oral and ventral suckers. 



Alimentary Canal. — The pharynx, lying at the base of the 

 oral sucker is rounded and thick-walled. Oil mm. in diameter. 

 It is followed by a moderately long, thin-walled oesophagus, 

 which, at its posterior end, becomes pretty wide. The intes- 

 tinal limbs are short, reaching to the middle of the body, 

 some distance beyond the ovary. 



Nervous System. — There is a pair of nerve-ganglia, one on 

 either side of the posterior end of the oral sucker, joined by a 

 thick, transverse commissure over the dorsal aspect of the 

 pharynx, with fine nerves given off anteriorly and posteriorly. 



Excretory System,. — The excretory vesicle is tubular, some- 

 whxt dilated near its posterior end (Fig. 70), reaching in 

 front to just behind the shell-gland and receptacuhim semi- 

 nis, where it ends in two shallow pockets (Fig. 71). It gives 

 off, in its course, a few fine tubes; and two, main, fine tubes 

 enter the anterior end, one to each pocket. The vesicle is 

 lined throughout by glandular cells, which project into its 

 lumen. 



Reproductive System. — The testes vary in shape, from 

 round to oval, measuring about 0195 mm. in length, or rather 

 less in diameter, when round in shape. The ovary, which is 

 rounded, is a little smaller than the testes (0-163 mm. in dia- 

 meter), but in a few cases, where the structure of the testes 

 does not appear quite normal, the testes are smaller than the 

 ovary. The testes vary a little in position ; they are more or 

 less symmetrically placed, dorsal and lateral, or somewhat 

 posterior to the ventral sucker (Fig. 69). The ovary is placed 

 behind the right testis, differing in this from D. sociale Liihe, 

 where it lies behind the left testis. In two cases, however, 

 there is a "situs inversus" or sexual amphitype (4, 5, 32, 36, 

 39, 55), and the ovary lies behind the left testis instead of the 

 right. 



The vasa deferentia are short (Fig. 74), entering the base of 

 the vesicula seminalis together ; the latter is a coiled tube. 



