ART. 7 CESTODE PARASITES OF BIRDS LINTON 43 



Tbe breadth of the anterior end of the longer proglottides is less 

 than that of the posterior end. Thus in a proglottis 0.14 mm. in 

 length the breadth of the anterior end was 0.16, of the posterior end 

 0.22; in another, 0.32 in length, the breadth of the anterior end was 

 0.42, of the posterior end 0.63. 



RECORD OF COLLECTIONS 



Gavia imnier: 



1911, July 22. — Fifty-nine strobiles and numerous fragments; 

 length 40 mm., more or less. 1911, July 24. 1. 

 U.S.N.M., Helm. Coll. 7880. 

 1911, September 1. — One hundred and thirty. 



1915, August 11. — Many. 



1916, July 4. — Four with scoleces, 2 without. 

 Golymhus holboelli^ new host : 



1913, April 28. — One fragment of strobile, length 15 mm. 



HYMENOLEPIS TRITESTICULATA (Fuhrmann) 



Figures 143-147 



Small cestodes refered to this species were found in the following 

 hosts: red-breasted merganser {Mergus serrator)^ surf duck {Oide- 

 Tuia fersficillatd) ^ white-winged scoter (6^. deglandi)^ greater scaup 

 duck {Marila 77mrila), and the American coot {Fulica mnericana). 



Scolex. — Varying in outline, but more or less triangular, suckers 

 relatively large, with thick borders; rostellum when fully extended 

 slender, cylindrical, much longer than scolex, sheath of rostellum 

 with strong muscular walls, and extending into the neck behind the 

 scolex; hooks 10, length 0.036 to 0.039 mm., with long dorsal and 

 short ventral root and slightly curved blade. 



Strobile. — Neck short, the segments in most cases beginning close 

 to the scolex ; in some cases, in which the anterior end of the strobile 

 was more or less relaxed, as if slightly macerated, the segmentation 

 is not distinct until 0.5 to 0.7 mm. back of the scolex. There is a 

 tendency in some strobiles to contract and thus increase the breadth 

 near the scolex, and rarely at other points. Thus, in one, the diam- 

 eter of the scolex in balsam is 0.19 mm., while the strobile immedi- 

 ately behind the scolex for a distance of 0.9 mm. has a breadth of 

 0.26. The strobiles in general are linear, increasing slowly in breadth, 

 the proglottides as a rule remaining much broader than long. The 

 male genitalia make their appearance early, exserted cirri having 

 been observed 1.5 mm. back of the scolex. The genital pores are 

 unilateral and are situated a little in front of the middle of the 

 lateral margin. The cirrus is armed with slender spicules. It is 

 more or less club-shape, and, when fully everted, a slight bulbous 

 enlargement may appear (fig. 147). The cirrus shown in this figure 



