EXAMINATION OF HELMINTHES 145 



the neck, a homogeneous portion of varying length, which terminates 

 in the head. In all Tseniidse, the head is furnished with four suckers 

 arranged radially (only to be made out in small species with a strong 

 lens or microscope), and, in the greater number, it is crowned with 

 a rostellum. This rostellum, which is frequently more or less 

 invaginated, varies considerably in shape and is furnished with hooks. 

 In Bothriocephalus, the head is elongated and possesses two longi- 

 tudinal furrows of varying depth, which are continued into the 

 suctorial grooves. Owing to the fact that the dorso-ventral diameter 

 is less than the transverse diameter, the head usually lies over on its 

 side v and for this reason the grooves appear to be placed laterally. 



The proglottides also show considerable divergence of form. Those 

 at the head end are broader than they are long, and they increase in 

 size and in structural development as they progress towards the tail 

 end. At the lateral margin of the larger Tsenise a slight eminence, 

 more or less distinctly denned, will be observed. This is the genital 

 papilla, with the genital opening at its summit. In the greater 

 number of species, the papillae alternate with comparative regularity; 

 in Hymenolepis, however, they are always placed at the edge of the 

 left margin, while in Dipylidium there are two genital openings to 

 each segment, placed one in the centre of either lateral edge. 



The genital pore is always furnished with two openings, those of 

 the cirrhus and the vagina, while in Dibothriocephalus there is a 

 third, namely, the uterine opening, from which the eggs are extruded. 

 In the other Taeniidse there is no uterine opening to the exterior, the 

 eggs being liberated only by the decomposition of the proglottides. 

 The three genital openings of Dibothriocephalus lie close behind one 

 another, in the middle line, upon that flat surface of the body which 

 is usually termed ventral. In well-preserved specimens they may be 

 seen with the magnifying glass, though they are less easily made out 

 in living material. 



The proglottides of all tapeworms vary according to their age, 

 which, as they are formed successively from the neck, is in direct 

 ratio to their distance from it. The youngest and narrowest pro- 

 glottides do not possess anything in the nature of reproductive organs. 

 These begin to appear in somewhat older segments, becoming more 

 developed the farther removed the segments are from the head. 

 Those in which all the sexual organs are fully formed are called 

 "mature." 1 As in most hermaphrodite animals, the male sexual 



1 'Proglottides with fully developed male and female organs are described in this 

 work as " mature." For those older proglottides, in which retrograde changes of the 

 sexual glands have already taken place and in which the uterus is filled with the oval 

 the term " ripe " is employed. TRANSLATOR. 



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