104 ILLINOIS BIOLOGICAL MONOGRAPHS [104 



intersegmental furrows are plainly marked. Shallow grooves and de- 

 pressions give the surface of the worm a somewhat roughened appear- 

 ance. The segments are firmly attached to each other. 



A common genital aperture (Figs. 69, 70, 71, 72, 172) is situated 

 near, or slightly anterior to, the middle of the margin of each proglottid. 

 Its position in the strobila alternates irregularly from side to side. There 

 is no genital papilla. 



The testes (Figs. 69, 72) lie in a single layer between the vitellaria 

 and anterior to the ovary. They are of ovoidal or spheroidal shape. In 

 length and breadth they measure 0.053-0.080-0.095 mm. by 0.05-0.07 mm. 

 In Schneider's drawing of his I. ocellata 50-60 testes may be seen, and 

 in preparations from either lot of his material about that number of 

 testes may be counted. He stated that the testes measure 0.10 by 0.06 

 mm. The vas deferens forms a thick straight mass of coils extending 

 from the end of the cirrus-pouch to the middle of the segment or even 

 a little beyond. In mature and ripe proglottids the vas deferens is 

 always well distended with spermatozoa. Extending into the segment at 

 right angles to the margin is the long and slender cirrus-pouch. This, 

 in a reconstruction (Fig. 74) from a transection, may be seen to curve 

 upward to the dorsal wall of the dermo-muscular sac where it is firmly 

 attached by strong muscle fibers. Its length varies somewhat in pro- 

 glottids of different stages of development and in different stages of 

 contraction. It measures 0.34-0.37-0.425-0.47 mm. long, the greater 

 lengths occurring in greatly contracted, and hence very wide, proglottids. 

 Schneider reported the ratio of its length to the proglottid breadth as 

 1 :3 in his I. ocellata and 1 :3-l :2 in his I. percae. The writer finds the 

 ratio in each of his forms to be from 1 :3 to 2 :5. In no case did the cirrus- 

 pouch reach to the middle of the proglottid tho at first sight the coils of 

 the vas deferens frequently gave it that appearance. Schneider saw the 

 protruded cirrus in I. percae, where it measured 0.1-0.2 mm. In both 

 of his forms he found the cirrus straight in the cirrus-pouch. The same 

 condition was observed by the writer. Schneider did not record having 

 seen a protruded cirrus and the writer failed to find such cirri in the 

 material examined. From the fact that the cirrus and the ductus 

 ejaculatorius form a straight tube in the cirrus-pouch one can safely 

 postulate that the protruded cirrus would be short. 



The vagina always opens dorsal to the cirrus-pouch. This is shown 

 by a reconstructed transection (Fig. 74) through this region. Then pass- 

 ing inward and bending slightly anteriad it crosses the cirrus-pouch ob- 

 liquely near the middle and passes toward the ventral wall of the dermo- 

 muscular sac. From the point of crossing the cirrus-pouch (Fig. 72) 



