12 OSBORN. [Vol. XVIII. 



cannot be sure that Poirier's account is not based on a variant 

 form like the one in Fig. c. 



Stafford '96 describes a cavity in Aspidogaster to which he gives 

 the name " cervicopedal pit," located between the " neck " and the 

 " foot," which runs backward some distance. A structure which 

 is possibly related to this is described by Nickerson '99 as occurring 

 in Cotylogaster occidentalis, where the front half of the body is 

 " capable of being retracted telescopically, into the body proper." 

 No such pit is found in Cotylaspis, as shown by sagittal sections 

 (Fig. 6), and there is no power of retracting the front part of the 

 body like that of Cotylogaster. 



e. The Cuticle. 



An unusually heavy cuticle envelops the entire worm and is 

 infolded at all the orifices, viz., those of the mouth, excretory 

 organs, marginal organs of the ventral sucker and the reproductive 

 organs (Figs. 6, 7, 8). It is thickest dorsally on the body, 15 //, 

 and thinnest in the acetabula of the ventral sucker, i ,a , and in the 

 mouth funnel. Owing to its thickness it is thrown into wrinkles 

 by the contractions of the animal, a longitudinal system appearing 

 when the body is thrust forward and a transverse system when it 

 is shortened (Fig. 2, a). It is as usual entirely devoid of cellular 

 elements, and rests directly upon the muscular layer of the body 

 wall. The outer portion is slightly darker colored than the inner, 

 but there is no line recognizable between these. At all of the open- 

 ings of the body the cuticle passes in and becomes directly con- 

 tinuous with the epithelium of the organ, as will be more fully 

 noted in connection with those parts. There are certain foreign 

 structures imbedded in the cuticle ; these are parts of the glands of 

 the parenchyma and certain structures which appear to belong to 

 the sensory nervous system and can be better considered later. 

 There are no hairs or hooks of any kind developed in connection 

 with the cuticle anywhere. 



/. Musculature of the Body-wall. 

 This has the usual form found in trematodes, and is much the 

 same as reported by Stafford in Aspidogaster and by Nickerson in 



