196 ILLINOIS BIOLOGICAL MONOGRAPHS [484 



course outside of the nerve strand for considerable stretches. Only one large 

 vessel, just within the nerve strand, passes into the base of the scolex on each 

 side. These two are quickly reduced in size and disappear at about the 

 middle of the scolex. In the youngest plerocercoids, such as shown in figure 

 50, there was seen at the posterior end a cuticular sac or invagination about 

 45m in length by lO^t in diameter, much resembling an excretory vesicle. But 

 since no vessels connected with this structure as in ^. rugosum, its nature was 

 not satisfactorily determined. On the other hand, the vessels of a young stro- 

 bila which had evidently just lost some segments did not open on the concave 

 posterior end but were lost in the parenchyma some distance from the end 

 after considerable anastomosing. 



The earliest traces of the reproductive rudiments appear in the marine 

 type about 45mm. from the tip of the scolex while the first eggs are to be seen 

 in the uterus 63mm, from the same point. The same data for a considerably 

 relaxed strobila from Coregonus clupeiformis are respectively 62 and 225mm. 

 Olsson (1893:17) found the first testes to appear in a 200mm. strobila from 

 Salmo alpinus 95m.m. from the anterior end, while 20mm. farther the uteri 

 began to show. Depending a great deal on the amount of relative contraction 

 of the proglottides, the genital cloaca is situated from one-third to half way 

 along the margin of the segment, altho Matz (1892:112) stated that its location 

 v/as between the first and second thirds of the edge of the proglottis. He also 

 said that they (? the cirrus-sacs) always opened on the left margin of the 

 strobila; but Liihe (1899) corrected this error by stating that altho they are 

 situated on one side for long stretches, in reality they alternate from side to 

 side. The writer also found them to be irregularly alternating but unilateral 

 Ihru m.any proglottides. In one strobila from a whitefish, for instance, they 

 vrere found to be arranged as follows, the numbers representing the numbers 

 ci proglottides in which they are on the same side before changing to the 

 opposite margin: 16, 3, 2, 5, 41, 21, 19, 7, 7, 8, 13, 3, 4, 11, 28, 9, 7, 9, 35, 10, 

 26, 9, 7, 9, 35, 11; while in a stretch of gravid proglottides from Cristivomer 

 namaycush, the lake trout, the data are: 27, 2, 80, 4, 3, 2, 13, beyond which 

 the cirrus-sacs had so degenerated that it was found impossible to follow them 

 ^vith satisfaction in the toto preparations. Zschokke (1884:25) erroneously de- 

 scribed the cirrus-pouch as being "... situee vers le milieu de la face ventrale 

 de chaque proglottis," while "L' orifice femelle se trouve en dessous, vers le 

 hord posterieur du proglottis," thus leading Lonnberg (1889:35) to establish 

 the new species B. suecicus which Matz (1892:111) considered with obvious 

 justification to be synonymous with his B. infundibulifortnis, or A. crassum as 

 it is now known. The cloaca itself is tubular, from 50 to 60ju in depth in the 

 fresh- water from and about 175^ in the marine form. In either case there is 

 no sharply separated hermaphroditic duct, the cirrus and vagina opening very 

 close together at the bottom of the pore, the latter constantly ahead of and more 

 or less ventral to the former. 



Matz stated that the testes were about 300 in number, 12ix in size, and ex- 

 tended from the median line to the lateral nerves, while Liihe (1900a) described 



