94 



ILLINOIS BIOLOGICAL MONOGRAPHS 



[94 



ularly arranged between vitellaria. Testes ovoidal, 0.05-0.095 mm. long 

 by 0.05-0.07 mm. broad, 50-60 in number. Vas deferens a thick straight 

 mass of coils; reaching to middle of proglottid or beyond. Cirrus-pouch 

 0.34-0.47 mm. long, slender, lying at right angles to margin of proglot- 

 tid. Ratio of length of cirrus-pouch to proglottid breadth 1 :3-2 :5. 

 Cirrus, when protruded 0.1-0.2 mm. long, when unprotruded, straight 

 within cirrus-pouch. 



Vagina always anterior and dorsal to cirrus-pouch, crossing cirrus- 

 pouch near middle. Vaginal sphincter small. Lumen of vagina ciliated. 

 Ovary bilobed, posterior. Lobes long and heavy. Vitellaria lateral, 

 follicular, denser near ovary. Uterus with 4-5-9 lateral outpocketings 

 on either side. Uterine pore single, situated near middle of proglottid. 

 Eggs provided with three membranes. Embryo 0.01 mm., second mem- 

 brane 0.0264-0.029 mm., outer membrane 0.031-0.037 mm. in diameter. 



Habitat : Intestine of Perca fluviatilis and other fish. 



1 In the course of this work specimens from Acerina cernua have been deter- 

 mined to belong to a new species, Proteocephalus cernuae. Outwardly these speci- 

 mens much resemble P. percae and there is therefore some doubt whether the 

 specimens collected by Pallas and the Taenia percae Miiller were identical. Such 

 a doubt is valid until modern investigations show that Acerina cernua harbors P. 

 percae (Miiller). 



2 Needs confirmation. 



3 This seems to be a misdetermination. The parasite was probably P. filicollis. 



