A TAPEWORM 81 



only then beginning to grow. The youngest proglottids are 

 those nearest the scolex ; those at the opposite end of the 

 body are the oldest and hence the largest. Count the proglot- 

 tids. The animal attaches itself to the wall of the intestine 

 by means of its scolex, which is provided for this purpose with 

 four suckers and usually two rows of chitinous hooks ; the scolex 

 of Taenia saginata lacks the hooks. Thus attached, it lies 

 immersed in the digestive fluids of its host and absorbs through 

 the outer surface of its body the nutriment it needs. It is with- 

 out a digestive system. 



Exercise l. Draw an outline of the animal on a scale of 4 or 5, 

 taking care to represent the number of proglottids accu- 

 rately. 



The scolex. Cut off the scolex, mount it on a slide in glycer- 

 ine or water, and examine it under the microscope. Notice the 

 fine excretory canals which occur in every part of it. Can you 

 determine their arrangement? Note the numerous minute 

 calcareous bodies. 



Exercise 2. Draw the scolex on a scale of 10. Represent accu- 

 rately the suckers and the number and position of the 

 hooks, if these are present. 



Exercise 3. Draw a single hook highly magnified. 



The proglottids. Each proglottid is composed mainly of repro- 

 ductive organs and circular, longitudinal, and oblique muscle 

 fibers imbedded in a spongy tissue called parenchyma. The 

 parenchyma fills the entire primitive body -cavity, which is thus 

 absent in this animal. Each proglottid contains a complete set 

 of both male and female genital organs. These are immature in 

 the youngest and smallest proglottids; in those at about a 

 third of the distance from the anterior end of the body they 

 are mature; in the largest proglottids, those at the posterior 



