THE CESTOIDEA 



133 



that it is with the " accessory suckers," and not with the bothridia 

 of the Tetraphyllidea, that they must be compared. They are, 

 therefore, homologous with the " proboscides " of Tetrarhyncha. In 

 a few cases, as Anopl. perfoliata (Fig. XXII. 6), vestiges of the 

 phyllidia are believed to be represented by the ear-like flaps at the 

 sides of the scolex, below the suckers. 1 



In the Anoplocephalinae the four suckers are at the apex of the 

 scolex, the apertures being directed forwards ; but more usually 

 they are laterally placed, and a rostellum is present, which may be 

 unarmed (as T. saginata) or armed, the armature consisting of from 

 one to four circles of hooks, which are generally of two sizes, 



..C 



FIG. XXIII. 



Longitudinal section of the rostellum of 

 T. crassicollis. a, the muscular mass of the 

 rostellum, below which are seen concentric 

 coats of muscle ; b, hooklet , c, ganglion 

 and transverse commissure ; d, longitudinal 

 (retractor) muscles of the hooklets ; e, 

 lateral nerve ; /, excretory canal. (After 

 Leuckart.) 



FIG. XXIV. 



The rostellum of Dipylidium caninum, 

 L., out of the cat (orig.); in the upper 

 figure, retracted ; in the lower, everted. 

 a, one of the suckers ; &, the spiniferous 

 region of the rostellum ; B, one of the 

 spines ; c, the apical aperture on the 

 scolex, through which the rostellum is 

 everted ; d, the region of longitudinal 

 muscles ; e, the region of circular muscles. 



arranged alternately (as in T. solium\ the shape, size, and number 

 of which afford valuable specific characters. In its simple form it 

 consists of a mass of muscles, acting on a cushion of connective 

 tissue, bearing hooklets (Fig. XXIII.) ; this muscular mass becomes 

 a hollow muscular sac, retractile into a pit (Fig. XXIV.). This 

 armed rostellum reaches its highest development in those species 

 of Taenia that inhabit birds, in which it consists of a muscular sac, 



1 The peculiar form Polypocephalus, Braun ( ? = Parataenia, Lint.), resembles the 

 Tetracotylea in the arrangement of the acetabula ; but is quite unique in possessing 

 sixteen "tentacles," capable of being withdrawn into a sac in the centre of the scolex 

 (Fig. XXII. 5). They appear to represent a rostellum. The habitat, in Trygon and 

 Rhinobatus, is exceptional for a Tetracotyleau, and but little is known of the 

 anatomy (Braun, 1878, and Linton (25), 1887). 



