DEFINITION OF T^NIA SAGINATA. 



407 



size and firm appearance. Especially characteristic is the breadth 

 of the middle segments, which amounts to 12 or 14 mm. The neck 

 seldom measures less than 1 to 1'5 mm. 

 Since the length of the segments increases 

 comparatively slowly, the great majority 

 are broader {sometimes three or four 

 times Iroader) than they are long; only 

 the ripe proglottides containing embryos 

 are (even in their contracted condition) 

 of the well-known melon-seed shape. The 

 large hookless head (1'5 to 2 mm.) has a 

 flattened crown, with a pit-like holloiu in 

 the middle, and has four large and very 

 powerful suckers, which, however, usually 

 project only slightly, and are frequently 

 mrrounded by a black, more or less broad, 

 pigmented border. In the mature proglot- 

 tides the same pigment is often found in 

 the vagina, vas deferens, and testes. The 

 complete development of the germ-producing 

 organs takes plccce at about the 600^/i 

 segment, while the embryos only attain ma- 

 turity 360 or 400 joints further on. The 

 nuviber of the so-called " ripe " segments 

 may be estimated at from 150 to 200. The 

 eggs have a thick shell, with a border of little 

 rods. They are generally markedly oval, 

 and almost always provided with the prim- 

 ordial yolk-skin. The uterus which encloses 

 them is characterised by the large number 

 {twenty to thirty) of its lateral branches, 

 which run out close beside each other, and 

 exhibit many dichotomous divisions. The 

 greatly projecting porus genitalis lies in the 

 ripe proglottides on the lateral margin, at 

 a perceptible distance behind the middle. 

 If, as often happens, the joints have been spontaneously liberated, they are 

 generally found vnthout eggs and shrivelled up, but still of cojisiderable 

 size and thickness. Before the evacuation of the eggs they generally^ 

 measure from 18 io 20 mm. in length and from 5 to 1 mm. in breadth. 

 The new formation and growth of segments take place so quickly, that 

 about eight, or even more, proglottides are separated daily, even ivhen, as 

 is the nde, only a singlQf^^^^j^f^^Qsoft® 



Fig. 237. — Toinia saginata 

 (natural size). 



