66 ILLINOIS BIOLOGICAL MONOGRAPHS [354 



transverse ridge between the bothria, which represents the tip of the scolex, 

 is also supplied with a number of small nerves from this irregular commissure. 



In ripe proglottides there are four main longitudinal excretory vessels 

 situated roughly in the median frontal plane, two at the extreme margins 

 of the medulla and two just within the nerve strands. Farther forward these 

 divide into three on each side. The middle one of each lateral trio then divides 

 dorsoventrally into two, while the innermost pair gradually diminishes in size 

 and are soon lost. This leaves three on each side, arranged as a triangle with 

 the base towards the median line and the apex outward. They pass into the 

 scolex and anastomose to form an irregular plexus. But this arrangement of 

 the main vessels is attended with a good deal of irregularity; nor is it the same 

 on both sides of the median line. For B. nylandicus Schneider described only 

 two main longitudinal trunks "which divide anteriorly into several canals and 

 form numerous coils, especially in the suckers. " The excretory system of B. 

 fallax according to Liihe (1900b :257) is like that described here in that there 

 is a triangle of vessels on each side anastomosing with each other and with the 

 nearest ones of the opposite side; but in adition it shows two other vessels 

 which "... verlaufen im Gegensatz zu den diinnwandigen Gefassen des 

 Plexus im Inneren der Markschicht, in der frontalen Medianebene, und zwar 

 der eine nach innen, der andere nach aussen vom Langsnervenstamm. Letzter- 

 er erinnert seiner Lage nach an die Verhaltnisse bei den Dibothriocephalinen, 

 insofem als die Mehrzahl der Hodenblaschen nach aussen von ihm liegt." 

 It will also be seen that the arrangement of the excretory vessels in this species 

 is quite different from that described by Linstow (1904:308) for B. pachycepha- 

 lus Linstow, in which species there are fourteen main vessels situated in the 

 cortical parenchyma among the longitudinal muscles. None of the specimens 

 were complete posteriorly so that the disposition of the system in the true 

 posterior end was not determined. 



The reproductive organs appear about 1.5mm. behind the scolex almost 

 completely developed. Thei^ openings are in the median line and, unlike 

 B. sturionis Duvemoy, all on the ventral surface, that is, on the same surface 

 towards which the ovarian isthmus is situated (cf. B. fallax Liihe, 1900:10 and 

 Cyathocephalus americanus, p. 57). Furthermore, while the male and female 

 openings are from 0.09 to 0.22mm. apart, the sets of genitalia up to 66 in num- 

 be, are 0.55 to 0.65mm. apart in the longitudinal direction, which distances 

 are, however, of no great specific value owing to the different degrees of con- 

 traction and relaxation of the strobila. The female genital cloaca is an irregu- 

 larly circular opening into which the vagina opens constantly close behind the 

 uterus, as in B. nylattdicus, but in the median Une, the uterine orifice being in 

 this case the one which is not exactly in line with that of the vagina and the 

 cirrus but alternates irregularly from side to side. There is a weakly developed 

 sphincter surrounding the common female cloaca. It seems, however, to be 

 at least partly confined to the vaginal opening rather than to that of the uterus. 



As in B. nylandicus, B. pachycephalus and B. cohaerens the testes are 

 situated in the medullary region and in two narrow lateral fields continuous 



