66 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



vol,. 56. 



anteriorly. The conical rostellum (fig. 65) is usually retracted, and 

 is 46 {x long and 54 [jl wide at the base. The middle and lower thirds 

 of the rostellum are covered with 6 circlets of hooks, which lie close 

 together and almost cover this portion of the rostellum. My Ameri- 

 can specimens, as shown in figure 65, have 100 or more hooks. The 

 hooks are rose-thorn shaped, those of the most anterior row being the 

 largest and those of the posterior row being the smallest. The ros- 

 tellum is continued posteriorly as a muscular mass, of which the 

 anterior portion is thinner and the posterior portion is oval. The 

 suckers are slightly prominent and are elongated longitudinally. 

 The neck is very short and is scalloped by an imperfect transverse 

 segmentation at the margin, these imperfect segmentations finally 

 becoming complete and forming the more anterior segments. The 



entire strobila is about 10 to 

 23.5 cm. long. The anterior 

 segments are short and are 

 followed by longer ones which 

 become almost square about 

 1.5 cm. posterior of the head. 

 About the middle of the 

 strobila they are elongated 

 longitudinally, becoming sev- 

 eral times longer than wide. 

 The longest segments are 

 about at the union of the 

 middle and posterior thirds 

 of the strobila, and are 6 to 7 

 mm. long and 1 to 1.5 mm. 

 wide. Posterior of this point 

 they become shorter, wider, 

 and thicker. The enlarged 

 posterior margin of each segment forms a sort of collar about the 

 smaller anterior margin of the succeeding segment. The primordium 

 of the genital pore forms on young segments as a small protuberance, 

 but in more mature segments this disappears and leaves instead a 

 small depression, which is posterior of the middle of the lateral 

 margin of the segment. The longitudinal excretory canals are very 

 prominent, even in young segments, and later show as wide wavy 

 canals; the transverse canals are likewise very wide and are situated 

 at the union of adjacent segments. 



Male genitalia. — The testes (fig. 66) are spherical, about 130 to 

 140 in number, and occupy nearly all the space between the longi- 

 tudinal canals not occupied by the other genitalia ; they are especially 

 numerous in the middle and posterior portions of this field and leave 

 a clear area in the anterior portion of the segment. The vas deferens 





^omm. 



Fig. 65.— Dipylidium sexcoronatum. Rostellum. 



