66 ILLINOIS BIOLOGICAL MONOGRAPHS [346 



small suckers and A. parvum is small and has relatively large suckers, 

 and this feature suggested the name Alassostoma. 



ALASSOSTOMA MAGNUM Stunkard 1916 

 [Figures 59 to 65] 



The material of this species consists of one worm from Pseudemys 

 troosti from Havana, Illinois ; one from P. elegans from the same locality ; 

 two from P. elegans from Chicago, Illinois ; and three specimens from an 

 unknown turtle from Marshall, Missouri. The first four specimens were 

 collected by the writer from the large intestine near its juncture with 

 the small intestine, and the material from Marshall, Mo.,bears the label, 

 "From cloaca of turtle." 



In the preserved state the worms are 10 to 12 mm. in length, 3 to 5 

 mm. in breadth, and 1.5 to 2 mm. in thickness. One specimen studied 

 in the living condition, measured 18 mm. in length when fully extended ; 

 preserved it is 11 mm. long, 3.8 mm. wide and 2 mm. thick. One fixed 

 specimen 10 mm. long and 3 mm. wide is not sexually mature. 



In the living state the worms are clear, hyaline, with the digestive 

 ceca visible as brown lines. Their movements are very slow. In shape 

 (Fig. 59) they are more or less oval, with the acetabulum forming 

 a slight caudal projection. The acetabulum is slightly sub-terminal, cir- 

 cular or ovoid, usually wider near the anterior than the posterior end. 

 The opening is necessarily relatively narrower than the sucker itself, in 

 one specimen the opening is merely a slit, 1.4 mm. long, 0.38 mm. wide 

 near the anterior end and posteriorly tapering to a point. In the largest 

 specimens the acetabulum is 2.5 mm. long by 2 mm. wide, and in the 

 smallest it is 2 mm. by 2 mm. 



The cuticular covering of the body is unarmed, and measures 10 to 

 12/*, in thickness. It is turned in at the openings of the excretory and 

 reproductive systems and lines the digestive tract to the bifurcation. 

 The dermo-muscular wall has the circular, longitudinal, and oblique layers 

 well developed and inside the oblique layer there is an additional layer 

 of longitudinal fibers (Fig. 60). Dorso-ventral fibers are scanty or 

 lacking and the parenchyma of the body r is very loose and vacuolated 

 (Fig. 64). 



Alimentary tract. — The oral sucker is terminal, spherical to ovoid 

 in shape, usually longer in the antero-posterior axis and somewhat wider 

 anteriorly than posteriorly. It is deeply set in the parenchyma of the 

 body and measures 0.9 to 1.35 mm. in length and 0.6 to 0.9 mm. in width. 

 Radial fibers pass from the external limiting membrane to the cuticula 

 lining the sucker; in a cross section thru the sucker (Fig. 65), the inside 



