254 



FLAT WORMS 



A tape-worm is divided into the segment-producing controlling head and the 

 series of segments or proglottides together known as the strobila. The head and neck 

 together form the scolex. Tape-worm heads are provided with suctorial or hook- 

 like organs, or both, to enable them to hold on to the intestinal mucosa. 



The hooks when present on the anterior extremity of the head are carried by a 

 protrusible structure called the rostellum. 



The importance of the head is generally recognized by the well- 

 known fact that the permanent evacuation of one of these parasites is 

 only arrived at when the head as well as the segments is expelled. 

 Otherwise, additional segments will be produced. 



10 



7-0% 



FIG. 67. Tape-worms. A. i, 2 and 3, Scolex, proglottides and ovum of Taenia 

 solium; B. 4, 5, 6 and 7, Scolex, prologlottides and ovum of Dibothriocephalus latus; 

 C. 8, 9, and 10, Scolex, proglottides and ovum of Taenia saginata. The onchosphere 

 in 10 is shown within the outer yelk coating (frequently seen in stools). In 3 only 

 the onchosphere within the embryonal shell is shown. 



Even in tape-worms twenty-five to thirty feet in length, the head is no larger 

 than a small shot. It carries the suckers or hooklets which best enable us to differ- 

 entiate the different species. The segments adjacent to the head are immature 

 the sexually-mature ones being found from the middle of the body onward. The 

 sexually-mature segment possesses a varying number of testicles: three in Hymeno- 

 lepis nana and as many as 2000 in Taenia saginata. As with the flukes, they also 

 have vasa deferentia, cirrus, ovaries, yolk glands, uterus, genital pore, etc. The 



