246 DR. R. T. LEIPER ox [Feb. 1, 



front of, and somewhat dorsal to the ventral sucker. It dis- 

 charges at its posterior limit by a short, straight, thick-walled 

 duct that runs out to the dorsal surface parallel to, and 025 mm. 

 behind Laurer's canal. 



9. Paramphistomum sellsi, sp. n. (Text-fig. 33.) 



The specimens contained in one of the tubes sent to me by 

 Dr. Sells showed such marked variations in shape that at first I 

 separated them into three well-defined groups, thinking that these 

 would prove on further study to represent distinct though closely 

 allied species. A comparison of serial sections of these forms has 

 convinced me, however, that they represent merely different 

 degrees of contractility in one and the same species. One stage 

 showed distinct dorso- ventral flattening approaching in appearance 

 the outline of a Polyclad Turbellarian. The second stage resembled 

 in outline an ordinary Amphistome with the ventral sucker 

 presenting wholly on the under surface. In the third stage the 

 worm assumed an elongated form not unlike an ear of wheat : the 

 posterior sucker having become completely everted and presenting 

 terminally. 



The parasite measures from 4 mm. to 6 mm. in length, and 

 varies considerably in breadth. The ventral sucker opens on 

 the under surface at the posterior end of the body, except in 

 greatly elongated examples as already mentioned. Its greatest 

 diameter is 0"53 mm., its cavity is 0*4 mm. in width, and the 

 musculature has an almost uniform thickness of 013 mm. 



The cuticle is but feebly developed all over the body, having a 

 thickness of less than O'Ol mm. Surrounding the anterior end 

 of the body are numerous fungoid papilla? arranged in parallel 

 rows. 



The pharynx is flask-like in shape, and is much less strongly 

 developed than in the other Amphistomes. It measures in length 

 - 35 mm., in breadth 0*27 mm., and its musculature has a depth 

 of only 0"1 mm. at its thickest part. There are no pharyngeal 

 pouches. 



The oesophagus is 0"5 mm. in length, O07 mm. in breadth, 

 with a very thin muscular sheath. 



The gut-branches are 02 mm. broad in front of the ventral 

 sucker, and end about the level of the fundus of the excretory 

 vesicle. 



The genital opening lies at the junction of the anterior third 

 with the rest of the body, and is situated at about 0*5 mm. behind 

 the bifurcation of the gut. There is a large genital atrium 

 exceeding in size the oral sucker and having an aperture of 

 03 mm. and a depth of 03 mm. : its muscular wall is 015 mm. 

 thick, and is sharply marked off from the parenchym. 



The testes lie in contact, one in front of the other, in the 

 posterior half of the bod^y, are oval in shape, and are not lobed ; 

 they have a diameter aritero-posteriorly of 1*0 mm. and dorso- 

 ventrally of 0-7 mm. 



