134 INFECTIOUS AND PARASITIC DISEASES. 



through the external covering. Depending upon the 

 species, the length of the worm varies from a few inches 

 (dwarf tape- worm) to thirty or more feet (Bothriocepha- 

 lus latus). The adult worm consists of a head or 

 scoleXj a thin thread-like neck, and a body made up 

 of conjoined segments or proglottides. The head is 

 provided with suckers, in some species with hooklets 

 also, by means of which the worm fastens itself to the 

 gut and maintains its position. It is on account of these 

 organs of attachment that the head is often difficult 

 to dislodge. Yet it must be expelled if a cure is to be 

 effected, since growth of the worm proceeds entirely 

 from the head end. The neck is unsegmented. Behind 

 the neck, the first segments are short and narrow, but 

 they gradually increase in size until the adult dimensions 

 are attained. The size of a segment is related to its 

 maturity. 



In each proglottidis are found both sexual elements 

 in various stages of development. The more mature 

 segments are situated towards the distal end of the 

 worm and contain numerous ova, in each of which is an 

 embryo worm. Segments containing embryos are said 

 to be "ripe," and it is these which are constantly sep- 

 arating from the less mature and being shed in the 

 stools. When they appear in the stools, two or more 

 segments are usually found attached together. These 

 may have the power of independent locomotion, a 

 fact which should not mislead the observer into believing 



