20 Earlc C. Stevenson 



EXPLANATION OF PLATES 

 Plate I. 



Fig. 1. A large hook of T. serrata. X 627. 



Figs. 2-4. Different views of the same small hook of T. serialis, show- 

 ing the shape of ventral root. X 310. 

 Fig. 5. Large hook of T. serialis. X 488. 



Plate II. 



Fig. 6. a. Large and small hooks of T. serrata. X 199. 



b. Large and small hooks of T. serialis. X 199. 



c. Large and small hooks of T. coenurus. X 199. 



Fig. 7. a, b, c, d, c. Different stages in the development of the hooks of 

 T. serrata. (a, b, c, e, after Leuckart, 1856; d, original drawing.) 



Fig. 8. A crown of hooks of Cystieereus piriformis. X HI- 



a, a small hook showing the lateral projection of prongs of ven- 

 tral root. 



Plate III. 



Figs. 9-19. Large hooks of T. serialis, showing the various shapes and 



outlines. X 242. 

 Figs. 20-23, Small hooks of T. serialis, showing different shapes and 



outlines. X 242. 



Plate IV. 



Figs. 24-31. Small hooks of T. serrata, showing different shapes and 



outlines. X 234. 

 Figs. 32-35; 43-46. Large hooks of T. serrata, showing different shapes 



and outlines. X 234. 



Plate v. 



Figs. 36-41. Small hooks of T. serrata superimposed to show the vari- 

 ation in relative position of homologous parts of different hooks 

 having the same magnitude a. X 234. 



Fig. 42. A small hook of T. serrata with prongs of ventral root widely 

 separated. X 234. 



Plate VI. 



Fig. 47. Side view of head of T. serrata, showing the hooks in situ, and 



the position of the suckers, also the first marks of segmentation 



of the strobila posterior of the head. X 40. 

 Fig. 48. Anterior view of the head of T. serialis, showing the crown of 



hooks and the position of the suckers. X 28. 

 Fig. 49. Same view of head of T. serrata, X 28. 

 Fig. 50. Portion of a section through the rostellum, cutting the hooks 



transversely, a. Cross-section of prong of a hook, cut just in front 



of the ventral root. 



2IO 



