598 L- R. ^'ARV, 



Part I. 

 Descriptive. 



A. The adult worm. 



The adult worm (Figs. 1 and 2) has been recorded as occuring- 

 in the cloaca of Frogs, Toads and Newts taken in manj^ localities 

 in North America. Leidy (1856), Pratt (1903) and Staffoed (1900) 

 referred this form to Amphistomum (Diplodiscus) suhclavatum. The 

 last mentioned author, in another publication (1905) established a 

 new species, Diplodiscus temporatm, for this form and gave a short 

 account of the most striking features of its anatomy. 



The sexuallj' mature specimens varj^ in length, when fullj' ex- 

 tended, from 2 mm to 6 mm. The average length is about 3,5 mm. 

 In such a specimen the width of the posterior sucking disc (Aceta- 

 bulum) is 1,4 mm; that of the body just anterior to the acetabulum 

 1,2 mm. The worms move about so actively that accurate measure- 

 ments while they are alive are obtained with difficulty, while on 

 being killed, even though they are previously narcotized, the con- 

 traction is so great that the measurements made from preserved 

 material are very misleading. 



The anterior end of the worm is narrow for about one third of 

 the entire lenght. From this point the width increases quite rapidly 

 to the extreme posterior end, at the junction of the acetabulum. 



The anterior sucker is situated at the end of the body and 

 opens forward. The large posterior sucker opens backward and 

 downward, so that the worm is considerable longer on the dorsal 

 than on the ventral surface. 



The body is covered with a thick, smooth, cuticular layer. 



Muscular system. 



The body wall has the usual systems of muscles; circular, 

 longitudinal and transverse. There are two sets of the last mentioned 

 fibres running in opposite directions. The circular muscle fibres are 

 extremely minute. Those of the longitudinal muscles, and of the 

 radial muscles are about twice the size of the circular fibres. In 

 none of my sections of adult worms, or cercariae, did I succeed in 

 demonstrating the muscular structures which have been described 

 and figured by Bettendoef (1907) as occuring in several forms of 

 the Malacocotylea, and in Polysfomum among the Heterocotylea. 



