324 ILLINOIS BIOLOGICAL MONOGRAPHS [324 



EXPLANATION OF PLATE 



Fig. 39- — Proteocephalus singularis La Rue, head, cross-section about 0.10 mm. 

 from the tip of the head, near the upper end of suckers. This section shows the 

 beginning of the muscle cross, mx, and the heavy muscles connecting the sucker 

 wall with the surface of the head. Figs. 39 and 40 are drawn to the same scale 

 as Fig. 41. 



Fig. 40. — Proteocephalus singularis La Rue, head, cross-section about 0.135 mm. 

 below tip of head and about middle of suckers. Shows heavy muscle across, mx, 

 with some fibers reaching out to the surface of the head between the suckers. 



Fig. 41. — Proteocephalus singularis La Rue, head, cross-section near lower 

 edge of suckers, showing muscle star, ins, with broadly flared ends. Nuclei are 

 shown as the larger black spots. The closely packed groups of short heavy lines 

 are tangentially cut ends of muscle fibers which attach to the suckers. 



Fig. 42. — Crepidobothrium gerrardii (Baird), vestigial fifth sucker, cross-sec- 

 tion. Note sucker cavity and musculature. Nuclei could not be seen in this tissue. 



Fig. 43. — Ophiotaenia filaroides La Rue, vestigial fifth sucker, from a frontal 

 section of a plerocercus. Note the sucker cavity filled with granules, basement 

 membrane, nuclei and muscle fibers in and around sucker. Compare structure of 

 vestigial sucker with that of the normal sucker beside it. 



Fig. 44. — Ophiotaenia filaroides La Rue, vestigial fifth sucker, frontal section 

 of head of plerocercus. Compare structures with those of Fig. 43. Scale should 

 read 0.05 mm. 



Fig. 45. — Ophiotaenia filaroides La Rue, vestigial fifth sucker from a cross- 

 section of head of a plerocercus. Note the sucker cavity filled with granules, the 

 basement membrane, the muscles, and nuclei. 



Fig. 46. — Ophiotaenia filaroides La Rue, vestigial fifth sucker, cross-section of 

 head of plerocercus. Note points mentioned for Fig. 45. Sucker cavity only 

 partly filled with granules. Scale should read 0.05 mm. 



