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 Tuenia 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. 
Bxercise 1. 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. 
Bxercise 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 
