58 ILLINOIS BIOLOGICAL MONOGRAPHS [346 



said only: "Das Verhalten, dass die Geschlechtsorgane altemirend dorsal und 

 ventral nach aussen miinden, erinnert in gewisser Beziehung, an die altemier- 

 ende marginalen Geschlechtsoffnungen verschiedener Fisch- und Vogeltaenien 

 und wurde bereits von den ersten Beobachter, Pallas und Batsch erkannt, d.h., 

 sie hatten auf beiden Flachen die fortlaufende Reihe der 'Punkte' wahrge- 

 nommen, ohne sie indessen als Ausmiindungen der Sexualorgane zu deuten. 

 Die neueren Beobachter haben sammtlich dieses oben beschriebene Verhalten 

 iibersehen, und geben die Geschlechtsoffnungen als ventral gelegen an." But 

 whatever is the stimulus which, during the very early stages of development 

 of the sets of genitalia from their rudiments, causes the reversal of the whole 

 proglottis, it would seem to be such at times as to fail to bring about the turning 

 over of all parts of the rudiment. As sho'\vn in figure 104, which is a diagram of 

 a sagittal series of seven proglottides including the terminal one, the cirrus 

 and female genital cloaca of number three from the top have gone to the oppo- 

 site surface while the ovarian isthmus, represented by the solid black disc in 

 each segment, has remained on the same surface as those in segments 1, 2 and 

 4 in the immediate neighborhood. Here the stimulus which brought about 

 the unisurficiality of the latter may have influenced the ovarian portion of the 

 common rudiment of number three and caused it to lag behind, while the more 

 peripheral rudiments of the cirrus, vagina and distal portions of the uterus were 

 freer to move. This arrangement of the parts in the aberrant segment in 

 question naturally causes considerable departures in the courses of the repro- 

 ductive ducts from the normal. 



The genital openings vary from 75 to 115^1 apart, but again as pointed out 

 by Kraemer these data are of very little specific value. The vagina and 

 uterus open into a common genital sinus or cloaca, but unlike conditions in the 

 European species the vagina opens constantly behind the uterus and slightly 

 to one side and not ahead of it. Furthermore, neither papillae nor sphincter 

 muscles are present around either or both genital openings in this species. The 

 female genital cloaca, usually situated at the bottom of a depression and often 

 on a low papilla, ranges from 30 to 60^i in depth. In frontal sections it is seen 

 to be in the form of a transverse slit about 60/x in length, into the ends of which 

 the vagina and uterus empty; that is, the vagina opens diagonally behind the 

 uterus and usually to the right of it. It is lined by a direct continuation of the 

 cuticula from the surface of the segment. The general habit of the reproduc- 

 tive organs is shown in figure 93, which is from a frontal section of a mature 

 proglottis. 



The majority of the testes are situated in the medullary parenchyma in two 

 fields lateral to the cirrus-sac, or more strictly speaking, in the lateral portions 

 of the region between the cirrus-sac and the ovary of the proglottis ahead, 

 since they usually extend forward to the latter and backward to the anterior 

 ends of the wings of the ovary of the segment to which they belong. While 

 their shape is usauUy spherical or somewhat flattened anteroposterior^ accord- 

 ing to the condition of contraction of the segment, their maximum diameter 

 is about 70/i. The coils of the vas deferens, altogether about 0.30mm. in dia- 



