64 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



vol.. 55, 



very short. Posterior of these the segments lengthen and become 

 almost square at a distance of 5 to 6 mm. posterior of the head. Pos- 

 terior of these they become elongate, attaining a maximum length 

 of 4 to 5 mm. and a maximum width of 2 mm. The posterior portion 

 of each segment is longer than its anterior portion and extends a 

 slight distance laterally to form the serrate margin. The terminal 

 gi-avid segments are pale yellow and are sometimes piriform, the 

 anterior portion being constricted and the posterior portion ex- 

 panded. The genital primordia develop comparatively early and are 

 recognizable 1 mm. behind the head in the twenty-fifth to the twenty- 

 seventh segments, the male genitalia being the first to become visible. 

 In mature segments (fig. 62) the genital pore lies posterior of the 



middle of the lat- 

 eral margin, and 

 is located in an in- 

 conspicuous de- 

 pression. The ex- 

 cretory canals are 

 visible just poste- 

 rior of the head 

 and become larger 

 and wavy in the 

 m ore developed 

 segments. 



Male genitalia. — 

 There are about 90 

 to 100 large testes, 

 which fill the an- 

 terior and poste- 

 rior portion of the 

 field between the 

 longitudinal ex- 

 cretory canals; there are but few testes in the portion of the field 

 near the female genitalia. The very much convoluted and looped 

 vas deferens lies anterior of the ovaries and meets the cirrus pouch 

 on the median side of the longitudinal canals. The cirrus pouch 

 is elongate piriform, with the dilation toward the median por- 

 tion of the segment; it is somewhat curved, with the convexity of 

 the curve directed toward the posterior portion of the segment, and 

 extends anteriorly and medially across the longitudinal canals. 



Female genitalia. — The ovaries are in the middle field of the seg- 

 ment and for the most part are posterior of the genital pores. They 

 are each composed of two lobes separated by the vagina, and each 

 irregularly lobulated. The vitellaria are smaller than either of the 

 two portions of each ovary and are likewise irregularly lobulated, 



Fig. 61. — Dipylidium 

 Head. Enlarged 

 VON RAtz, 19009. 



OERLE-iq. 



After 



Fig. 62.— Dipylidium OERLEYi. Ma- 

 ture segment. Enlargeb. Af- 

 ter VON RAtz, 1900o. 



