170 ILLINOIS BIOLOGICAL MONOGRAPHS [170 



while a fifth apical sucker is 0.130 mm. in diameter. Muscles of sub- 

 cuticular layer are as usual. The heavy layer of longitudinal muscles 

 below the subcuticula in the anterior part of the worm is very strongly 

 developed, filling up almost the entire space in unripe proglottids. 

 Dorsoventral muscles are very heavily developed. In anterior segments 

 the main longitudinal nerves lie about 12 /i 00 > an d in ripe segments about 

 Vioo> °f the segment width from the lateral margins. Mesad of the 

 nerve trunks lie the excretory ducts two on either side. Chalkbodies 

 are lacking entirely. 



Sexual openings are marginal, irregularly alternating, posterior to 

 the middle in each proglottid. The vagina lies anterior to the cirrus. 

 The cirrus is cone-shaped, blunt at the tip, 0.141 mm. long. The point 

 is 0.042 mm. broad. The cirrus-sheath extends %-% across the breadth 

 of the proglottid. The vas deferens makes many coils before entering 

 the cirrus-sheath. Testes are very numerous, 0.053-0.083 mm. in diam- 

 eter. From von Linstow's figure one may conclude that there are about 

 70-100 testes. The vagina runs in a curve to the middle of the posterior 

 region of the segment where it forms many coils anterior to the ovaries. 

 These coils function as a receptaculum seminis. The ovary is made up 

 of two groups of club-shaped bags which run parallel to the posterior 

 margin of the proglottid. Anterior to its middle lies an oocapt. Vitel- 

 laria are follicular, reaching on left and right the full length of the 

 proglottid inside the longitudinal muscles. The uterus in the posterior 

 part fills the whole space within the longitudinal muscle fibers and 

 extends anteriad in round diverticula. In von Linstow's drawing which 

 is reproduced (Fig. 177) there are 6-8 diverticula on either side. Eggs 

 are globular, 0.027 mm. They have two membranes, the outer one very 

 delicate and hyaline. The six-hooked embryo measures 0.021-0.023 mm. 

 in diameter. 



Habitat: Intestine of Acipenser stellatus (type host); River 

 Giirgen, Caspian Sea (type locality). Von Linstow failed to state who 

 collected the specimens of this species and the abundance of their 

 occurrence. 



This species is one of the more robust Proteocephalids and is thus 

 distinguished from a large number of species of the genus. The fact 

 that the vagina forms many coils anterior to the ovary and that the 

 ovary consists of slender club-shaped bags separates it effectively from 

 all other known species. The position of the genital pore posterior to 

 the middle of the proglottid is a further distinguishing feature. In 

 many respects this species most closely resembles P. fossatus (Riggen- 

 bach). 



