690 DAVID HILT TENNENT. 
Fic. 50.—Tangential section through body wall of Gasterostomum 
gracilescens, showing spines imbedded in the cuticle and the four sets of 
muscles lying below the body wall. 
Fic. 51.—Longitudinal oblique section through one of tails of Bucephalus. 
The section passes through two longitudinal muscle bands. 
Fic. 52.—The reproductive organs of Gasterostomum gracilescens, 
seen from the left side. Diagrammatic. 
Fic. 53.—Longitudinal section through the digestive system of Gastero- 
stomum gracilescens. mth. Mouth. 
PLATE 42. 
Fic. 54.—Dorso-ventral longitudinal section through the anterior end of 
Gasterostomum gracilescens. 
Fic. 55.—Transverse section through penis and penis sheath of Gastero- 
stomum at the level of the union of the uterus with the genital atrium. 
Fic. 56.—Longitudinal section of the posterior end of the body of Gaste- 
rostomum gracilescens. 
Fic. 57.—Transverse section of Gasterostomum gracilescens taken 
just behind the sucking disc. 
Fie. 58.—Tangential section through wall of gut in Gasterostomum 
gracilescens. 
