ART. 7 CESTODE PARASITES OF BIRDS LINTON 49 



HYMENOLEPIS. species 

 Figures 157-159 



In a small lot of oestodes, collected by Kobert A. Goffin, Nov. 20, 

 1920, from Fulica americana (U. S. N. M., Helm. Coll. 7885,) one 

 small strobile differs from the others, which have been referred to 

 H. tritesticulata. 



Scolex. — Subtriangular in outline; suckers oval, a little longer 

 than broad; sheath of rostellum pyriform, extending a little way 

 back of posterior margin of the suckers; hooks (fig. 158) 10 in num- 

 ber and about 0.036 mm. in length, with conspicuous air spaces. 



Strobile. — Neck very short, narrower than scolex ; first segments 

 very short; rudiments of genitalia appear as early as the segments; 

 Mature cirrus-pouches appear about 1.25 mm. back of the scolex; 

 cirrus-pouch short-fusiform, with thick muscular walls, more or 

 less curved; in some the convex side is anterior, in some posterior, 

 others are more or less curved dorso-ventrally. The genital pores 

 are unilateral, and near the anterior border of the proglottis. The 

 cirrus is smooth, slender, filiform, almost spiculate; when fully 

 everted it is seen to issue from a short, subconical base (fig. 159). 

 Length of cirrus-pouch 0.012, diameter 0.04. The genitalia are not 

 very clearly shown in the mounted specimen. The three globular 

 testes, about 0.021 mm. in diameter, are placed in a horizontal line 

 near the posterior margin of the proglottis, two of them in contact 

 with each other at the median line, the other slightly removed to- 

 ward the antiporal margin. There is a seminal vesicle near the 

 inner end of the cirrus-pouch. Vagina not satisfactorily shown; 

 ovary not distinct, but appears to be relatively small, slightly lobed, 

 the larger part of it on the antiporal side of the median line; 

 uterus somewhat tubular in ventro-posterior part of proglottis, later 

 it occupies the greater part of the medullary space. 



Dimensions, in balsam: length 5.6 mm.; breadth of scolex 0.19; 

 length of sucker 0.114, breadth 0.084; maximum diameter of sheath 

 of rostellum 0.075; distance to first segment 0.09, length 0.006, 

 breadth 0.11 ; length of cirrus-pouch 0.09 to 0.12, maximum diameter 

 0.03 to 0.04; cirrus, basal portion, length 0.012, breadth 0.012, slen- 

 der portion, length 0.045, diameter 0.004; posterior .segments, length 

 0.10, breadth 0.28. 



RHABDOMETRA SIMILIS (Ransom) 



Figures 160-163 



Scolex. — The shape of the scolex varies somewhat, due to different 

 states of contraction when fixation took place. In most cases it is 



