82 INVERTEBRATE ZOOLOGY 
end of the body, the uterus is so distended with eggs that most 
of the other genital organs are obliterated and do not appear. 
A pair of longitudinal excretory canals passes from one end of the 
worm to the other, running near to and parallel with each lateral 
edge; in each proglottid, also, are one or two transverse canals. 
One or more pairs of longitudinal nerves run parallel with and 
very near the excretory canals, which are also joined in each 
proglottid by a ring commissure. 
Cut off two or three proglottids from the forward end of the 
body, two or three from about a third of the distance from the 
anterior end, and two or three from the posterior end, and soak 
them all first for a short time in a solution of caustic potash and 
then in one of equal parts of glycerine and water. 
Place the proglottids from the hinder end of the body in 
dilute glycerine between two glass slides, press them gently so 
as to squeeze them as thin as possible without crushing them, 
and study them under the microscope. In the middle of 
one of the lateral edges of the proglottid notice a slight pro- 
jection containing a depression. This is the genital papilla, and 
the depression is the genital cloaca. Two canals will be seen 
running from the genital cloaca toward the center of the pro- 
glottid. These are the vas deferens and the vagina, the former 
being the larger of the two. The greater part of the proglottid 
will be seen to be occupied by a much-branched organ filled 
with a granular substance. This is the uterus, and the granules 
are eggs. Near each lateral edge of the proglottid will be seen 
a straight band. These two bands are the dorsal excretory canals ; 
find the transverse canal near the hinder end of the proglottid. 
Between each canal and the edge of the proglottid will be seen 
a delicate line running parallel with the canal. These are the 
main nerves; they are joined by transverse nerves. 
Exercise 4. Draw the proglottid, showing accurately all of these 
features that you have observed. 
