66 PHYLUM VERMES 



outer surface of its body the nutriment it needs. It is without 

 a digestive system. 



Exercise 1. Draw an outline of the animal on a large scale, taking 

 care to represent the number of proglottids accurately. 



The Scolex. Cut off the scolex, mount it on a slide in glycerine or 

 water, and examine it under the microscope. Notice the fine excre- 

 tory 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 lo. Represent accurately 

 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 obHque muscle 

 fibers embedded in a spongy tissue called parenchyma. The pa- 

 renchyma 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 end of the body, 

 the uterus is so distended with eggs that most of the other genital 

 organs are obliterated and do not appear. Two pairs of longitudi- 

 nal excretory canals pass 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 dilute 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 



