22 GUIDE TO THE STUDY 



vitelline duct runs forward from this to the Mehlis gland. From 

 this point the uterus passes forward as an unbranched tube in the 

 mesal line, extending to the anterior end of the proglottis. The 

 female organs are confined to the ventral surface of the 

 proglottides. 



At either side of the proglottis may be seen two clear lines. 

 The inner, larger of these represents the main canal of the 

 excretory system. Close to the posterior margin of each proglottis 

 is a transverse canal connecting the longitudinal canals. A 

 second, much smaller longitudinal canal lies entad of the above 

 described and may be seen in sections. 



Outside of the excretory canal is the principal longitudinal 

 nerve, on each side. Smaller nerves are present but cannot be 

 seen in whole mounts. 



The excretory and the nervous system are continuous through- 

 out the length of the strobila. 



Ripe Proglottides.— In the terminal segments the generative 

 organs have been in large part supplanted by the uterus, which 

 has become much branched and is filled with eggs already 

 containing the six-hooked or hexacanth embryo. The number 

 and form of the branches of the uterus are points of importance in 

 classification, there being eight to ten irregular ramifications on 

 each side in Tcenia pisiformis. 



Examination of Sections.— Cross-sections through a mature 

 proglottis emphasize the lack of alimentary canal and of body 

 cavity, a condition typical of the Cestoda. The outermost 

 layer of the body is a thick resistant cuticle, which is secreted by 

 prominent, deeply staining, fusiform matrix cells embedded in the 

 parenchyma, or tissue which fills all the space between the 

 different organs and muscles. Immediately under the cuticle 

 is a delicate layer of circular muscles, followed by a layer of 

 longitudinal muscles whose cut ends can be seen among the 

 matrix cells at their outer end. A second and much more exten- 

 sive set of longitudinal muscles lies in the parenchyma entad of 

 the matrix cells. Within these are the transverse muscles which 

 run across the proglottis. Scattered through the parenchyma 

 are the light-refracting, concentrically striated calcarious bodies 

 which give to the worm its opaque white color. 



The large pore near the lateral margin of the section is the 

 external excretory vessel in cross-section. Immediately entad of 

 this is the smaller internal excretory vessel. Lying just outside of 



