53] PROTEOCEPHALIDAE — LA RUE 53 



to the middle of the proglottid. It is ovoidal with its broadest part at 

 the inner end. Its wall is thick, thickest at the outer end. 



The ovary is bilobed, the lobes being oval in shape with smooth 

 outlines. The vitellaria are lateral, longitudinal, follicular glands 

 which lie just inside of the lateral ducts. Oviduct, ootype, and other 

 organs of the interovarial space are as in other species of the genus. 

 The vagina (Fig. 185) always lies anterior to the cirrus-pouch. It 

 widens slightly and again narrows in its course to the middle of the 

 proglottid. Near the inner end of the cirrus-pouch it bends posteriad 

 and thence takes a direct course to the interovarial space where it forms 

 several coils. The uterus (Fig. 174) containing eggs is made up of 

 4-6-8 lateral pouches which in fully ripened segments fill up the space 

 between the vitellaria. 



The excretory system is of the usual type. Two pairs of lateral 

 excretory ducts take their origin in the head region. They empty into 

 a small bladder situated at the base of the last proglottid. No second- 

 ary openings were observed in the head but they were found in the 

 posterior region of each proglottid. 



The eggs have a diameter of 0.037-0.038 mm. Barbieri failed to 

 state whether this measurement included only the embryo or embryo 

 with its membranes. Larval stages were found in Bythrotrephes and 

 Leptodora. 



This species, as will be seen from its position in the tables at the 

 end of this section, is most closely related to P. esocis (Schneider). It 

 is differentiated from that species by its different proportions, by its 

 much smaller and more numerous testes, by the position of the coils of 

 the vas deferens and by the relation of the vagina to the cirrus-pouch. 

 P. agonis while resembling P. filicollis in size differs from that species 

 in having a longer cirrus-pouch, in the excentric position of the coils of 

 vas deferens, and in having smaller and more numerous testes which 

 lie in one layer. P. agonis is readily distinguished from P. fallax, P. 

 dubius, P. pusillus, and P. exiguus by its lack of a fifth sucker, by its 

 more numerous and smaller testes, and by its less numerous uterine 

 pouches. 



