77] PROTEOCEPHALIDAE — LA RUE 77 



tions and the connections of which can be worked out only in recon- 

 structions of sections. The uterus is a median tube in mature proglot- 

 tids. In ripe proglottids (Fig. 56, 179) there are 6-8 lateral pouches 

 on either side of the median tube. These lie in the ventral field and 

 come to occupy nearly the whole proglottid. By the pressure of the 

 densely packed uterus the vitellaria are pushed farther toward the mar- 

 gins ; the testes are pushed close to the dorsal surface and the shrunken 

 ovaries are crowded into a small triangular space in the posterior part 

 of the segment. The ripe proglottid is practically a thin walled sac 

 divided up into compartments by the thin septa of the uterine pouches. 



The eggs are discharged through 2-3 uterine pores (Figs. 56, 179) 

 or through a rift down the ventral surface which is caused by a further 

 splitting of these uterine pores. The usual number of uterine pores is 

 2 or 3 but occasionally a proglottid is found with a single pore. Krae- 

 mer describes a single uterine pore in the middle of the segment. The 

 eggs have a shell with three membranes, the outer hyaline, variable in 

 size, a middle heavier and more granular membrane, and an inner thin 

 membrane enclosing the embryo. The embryos measure 0.031-0.0336 mm. 

 in diameter. Such a wide variation is probably due to the different 

 forms which the embryos assume. Some are spherical, others ovoidal. 

 The middle membrane measures 0.036-0.041 mm. These measurements 

 show very well the limits of variation. The outer membrane was not 

 measured. 



This species is readily differentiated from P. percae by its smaller 

 head and suckers, more slender neck, and smaller proglottids. It is less 

 robust than P. percae. It differs from P. percae in having a much 

 shorter cirrus-pouch, fewer testes, a shorter ovary, and larger embryos. 

 It is readily distinguished from P. torulosus by its smaller size and by 

 its lack of a fifth sucker. It differs from the P. longicollis (Rud.) as de- 

 scribed by von Linstow in having a smaller head with much smaller 

 suckers. In the P. longicollis of von Linstow the testes are much larger 

 than in P. fallax and they are in two (?) fields. The cirrus pouch is 

 shorter in P. longicollis. The lateral pouches of the uterus are fewer in 

 number and the embryos are smaller than in P. fallax. P. fallax varies 

 from the P. cernuae in being more slender, with a smaller head and less 

 muscular suckers. The latter species has broader but narrower pro- 

 glottids, a shorter cirrus-pouch, more numerous and much larger testes, 

 a longer span of ovary, and smaller embryos. P. fallax differs from P. 

 filicollis (Rud.) in being longer, in having a fifth sucker, a longer cirrus- 

 pouch, fewer testes, and larger embryos. 



P. fallax much resembles P. exiguus but it differs from that species 

 in having a larger head, larger suckers, a larger fifth sucker, a longer 



