80  ILLINOIS BIOLOGICAL MONOGRAPHS [80 



the genital atrium directly dorsal to the cirrus-pouch. Near its opening 

 there is a small sphincter vaginae 0.016 mm. long by 0.010 mm. thick. 

 Normally in its course the vagina is slightly bowed posteriad across the 

 middle or the inner end of the cirrus-pouch. The course of the vagina 

 in toto preparations cannot be traced to the interovarial space. The 

 organs of the interovarial space have not been studied. The embryos 

 measured 0.026-0.0265 mm. in diameter, the outermost envelope 0.042- 

 0.047 mm. The second membrane was not measured. 



In some respects the present species resembles P. fallax La Rue. 

 The triangular shape of the interovarial space of ripe proglottids is much 

 alike in the two species. So also there is considerable resemblance in 

 respect to the uterine outpocketings. The proglottids, however, are as a 

 rule broader and shorter in the present species. In the number of the 

 testes and their close proximity to each other this species is very differ- 

 ent from P. fallax. The cirrus-pouch tho greatly resembling that of P. 

 fallax is relatively shorter. The two species are alike in the character 

 of the vagina and the sphincter vaginae. Ovaries are larger in the pres- 

 ent species. The best characters for distinguishing the two species are 

 the number and size of the testes, the relative size of the cirrus-pouch 

 and the size of the embryos. In some respects this species resembles P. 

 duhius La Rue but the ripe proglottids are a little larger and somewhat 

 thicker in the present species. The cirrus-pouch in proglottids of the 

 same stage of development may be of nearly the same length. This 

 species has more testes and these are smaller than in P. dubius. The 

 chief difference lies in the size of the embryos. This difference amounts 

 to 0.005-0.007 mm. The second membrane of the eggs of P. dubius is 

 larger than the outer membrane of eggs of P. neglectus. 



The present species differs from P. percae in the length of the cir- 

 rus-pouch, in the proportions of the proglottids, number and size of the 

 testes, and in the size of the embryos. P. neglectus differs from P. lon- 

 gicollis as described by v. Linstow in the number, size and arrangement 

 of the testes. The arrangement of the testes of P. longicollis in two 

 fields sets that species apart from all the other species reported from 

 fish, if von Linstow 's observations on that point are correct. P. neg- 

 lectus further differs from that species in the number of uterine pouches 

 and in the position of the genital pore. P. neglectus does not agree well 

 with Zschokke's (1884:14-16) description of Taenia longicollis Rud. 

 from Coregonus fera. The form which he described is apparently iden- 

 tical with the P. fallax La Rue which occurs in the same host species. 



