74 MORPHOLOGY OF INVERTEBRATE TYPES 



immense quantity of eggs. The entire chain of proglottids is 

 strongly compressed dorso-ventrally, but owing to the lateral 

 position of the genital openings the distinction between the dorsal 

 and ventral surfaces is not so simple as is the case with tape- 

 worms in which the uterus has an opening of its own in the 

 median ventral line. It is customary to call dorsal the surface 

 which is further removed from the ovary. 



The scolex is almost square in a transverse section and com- 

 pared with the chain is very small, for it measures only about 

 1.5 mm. square. It has four suckers and between them a poorly 

 developed and modified rostcllum appearing as a small sucker. 

 Besides a highly developed muscular system it has a central 

 nervous and an excretory system, both of which continue 

 through the entire chain of proglottids. 



The mature proglottids are most suitable for the study of the 

 internal organization of the tapeworm for only in them all parts 

 of the reproductive system are found. An examination of a 

 cross-section shows that the outside covering is a cuticle pro- 

 duced by special cells situated in the parenchyma or the tissue 

 which fills out all the spaces between the different organs and 

 muscles. An epithelial epidermis is lacking. The muscular 

 system is highly developed. It consists of a thin sheet of circular 

 muscles followed by a thin sheet of longitudinal muscles beyond 

 which are the cuticle-producing cells. A second set of longitu- 

 dinal muscles extends all the way to the transverse muscles which 

 run from one side of the proglottis to the other. Dorso-ventral 

 muscles traverse the parenchyma and serve to flatten the body. 

 The central portion inclosed between the dorsal and ventral 

 transverse muscles contains all the organs with exception of the 

 peripheral nerves, four of the longitudinal nerves and the col- 

 lecting tubules of the excretory system. The parenchyma is a 

 mesenchymatous tissue and its cells produce usually calcareous 

 bodies found in great quantities throughout the parenchyma. 



Digestive organs are absent. 



The nervous system consists of ten longitudinal nerves, three 



