76 ILLINOIS BIOLOGICAL MONOGRAPHS [y^\ 



followed as well, while close to the scolex they lose their identity and break up 

 into a plexus of very small vessels which ramifies forward thruout the latter. 

 In the posterior border of the scolex, however, a small branch on each side 

 takes a straight course just within the nerve strand for a short distance. 

 Flame-cells are quite numerous and readily discernible especially in the medul- 

 lary parenchyma. In young strobilas where no segments have yet been lost, 

 two comparatively large excretory vessels pass backward to the posterior end 

 and empty into a small narrow terminal vesicle. This in a larva 12.4mm. in 

 length was found to be 40/x long by 10^ wide, while the diameter of the excre- 

 tory vessels was ISju. 



The earUest traces of the reproductive organs in the form of a transverse 

 line in either half of the proglottis (the rudiments of the vagina, cirrus-sac and 

 lateral portions of the vas deferens) appear from 4 to 10mm. from the tip of the 

 scolex, while the first eggs are seen in the uterus-sacs from 25 to 35mm. from 

 the same point. The development of all of the genitalia is very gradual and 

 can be easily followed in good toto preparations, since the diagrammatic nature 

 of the worm, above mentioned, extends to the reproductive system, making 

 this species an ideal one for study. The cirrus and vagina open into a common 

 genital cloaca, which is situated in the middle of the margin of the proglottis, 

 while the uterus opens oh the ventral surface, not in the median line but towards 

 the side occupied by the atrimn. The cloacae alternate irregularly from side 

 to side, from one to ten having been found occupying the same margin in 

 successive proglottides. The following figures represent the number of such 

 segments before the genital aperture changes to the other side in the fifth 

 specimen of the above table: 1, 2, 1, 8, 1, 1, 1, 2, 2, 3, 3, 1, 2, 2, 10, 1, 1, 1, 3, 

 3, 2, 2, 1, 4, 1, 1, 2, 2, 3, 2, 2, 3, 6, 6, 1, 1, 1, 1, 1, 3, 2, 1, 3, 3, 2— as far forward as 

 the rudiments could be conveniently traced. The genital cloaca (Figs. 100, 101) 

 is elliptical in outline when viewed from the side, its longer diameter being 

 directed dorsoventrally, while in transverse sections it is squarish in outUne. 

 The dorsoventral diameter, longitudinal diameter and depth are, respectively, 

 70 to 85m, 40 to 55m and 40 to 60^. Into the middle of the bottom of this 

 depression opens the hermaphroditic duct which is about 60/x in length, into 

 the bottom of which in turn opens the vagina immediately ahead of the cirrus. 

 Since the cirrus proper is a long slender tube and since the external portion 

 of the hermaphroditic duct is usually found quite tightly closed and the end 

 of the cirrus turned around toward the opening of the vagina, self-impregnation 

 would seem to be quite probable in this species. On the other hand, the fact 

 that the genital cloaca is so well formed and further that it is surrounded by a 

 well developed sphincter and a series of muscular fibres radiating out into the 

 surrounding parenchyma, as shown in figures 100 and 101, argue in favor of its 

 use in cross-fertilization. No protruded cirri were seen, however, in the material 

 at hand. Perhaps both methods of fertilization occur. 



The testes are spherical to elhpsoid?,l in shape, their longest diameters 

 being dorsoventral, while their cross-sections are usually cu'cular in outUne. 

 In segments where there are as yet only a few eggs in the uteri their dorsovcn- 



