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. 



