PHYLUM PLATYHELM1NTHES 



233 



of the hooks varies accordingly : when the rostellum is fully 



retracted the points of the hooks are directed forwards, and may 



even meet in the centre ; as the rostellum 



is protruded the hooks become rotated until 



their apices come to be directed backwards. 



Four cup-shaped suckers project slightly 



from the surface behind the circlet of 



hooks. 



The body or strobila has a jointed appear- 

 ance, owing to its being made up of a 

 string of segments, or proglottides about 

 850 altogether. These are narrower and 

 shorter in front, gradually increasing in size 

 towards the posterior free extremity. The 

 neck or part immediately following the head 

 is devoid of any trace of segmentation. The 

 two surfaces of the proglottides are not to 

 be distinguished by any differences visible 

 to the unassisted eye ; but that side to- 

 wards which the female reproductive organs 



are more nearly approximated is regarded as the ventral, the 

 opposite as the dorsal surface. On one border, sometimes the 

 right, sometimes the left, of each proglottis, is a little prominence, 

 the genital papilla, on which is the opening of a chamber, the 

 genital cloaca, into which both the male and female reproductive 

 ducts open. 



An examination of entire living, and of preserved and stained 

 Tape-Worms under the microscope shows (1) that an alimentary 



. LSI. Head of Tsenia 

 solHim. magnified. 

 (After Leuckurt.) 



Fu;. lisi. Transverse section of Taenia solium. (After Shipley.) 



system is not present : (2) that nervous and excretory systems are 

 represented ; (3) that there is a complete set of reproductive 

 organs, constructed on the same general plan as those of the 

 Liver-Fluke, present in each of the proglottides. 



The nervous system consists of two not very well-defined 

 f/anr/lia. united by a broad transverse commissure in the head ; of 



