18 PROCEEDINGS OF THE NATIONAL MUSEUM vou 70 



Larus argenfatus^ new host: 



1912, September 4. — Three small, longest about 9 mm., in 

 formalin. 



DILEPIS UNILATERALIS (Rudolphi) 



Figures 45-51 



Scolex. — Short and broad; suckers orbicular, directed forward; 

 rostellum short and stout, armed with two circles of hooks, 10 in 

 each circle; length of hooks in anterior circle about 0.033 mm., in 

 posterior circle, about 0.018 ; hooks with long basal and short ventral 

 roots, blade moderately curved. It is difficult to determine the num- 

 ber and arrangement of the hooks on the retracted rostellum. One 

 scolex was found among the mounted specimens with everted rostel- 

 lum (fig. 46), from which the above details were obtained. 



Strobile. — In most cases this is much narrower than the scolex for 

 a short distance. It then increases in breadth, usually rather 

 quicldy, in some cases almost abruptly; nearly linear throughout; 

 breadth of the posterior end of a proglottis greater than the anterior, 

 imparting a more or less serrate outline to the lateral margins; 

 genital pores unilateral, near the anterior end of the proglottis. 

 In many cases the genital pore is at the summit of a papillary pro- 

 jection. The cirrus was seen exerted in only a few instances. It is 

 relatively long and slender, and is armed with minute spines. The 

 cirrus-pouch is elongate, subcylindrical, and reaches to about the 

 median line, its inner end acting as a seminal vesicle. At its base 

 near the median line, and at the anterior end of the proglottis, there 

 is a voluminous vas deferens. The testes are about 10 in number, 

 although 12 were counted in a few proglottides. They are situated 

 behind and along the lateral margins of the ovary. In some adoles- 

 cent proglottides two or three of the testes lay nearly in front of the 

 ovary on the antiporal side. The vagina opens on the ventral side of 

 the cirrus and lies a little posterior to the cirrus-pouch, turning dor- 

 sad in the vicinity of the vas deferens. It has thick, muscular walls, 

 and is surrounded by a layer of what appear to be glandular cells. No 

 seminal receptacle was seen. The ovary is relatively large, is com- 

 posed of two lateral divisions, deeply lobed and united by a trans- 

 verse portion at the median line. The vitelline gland is compact, 

 and situated at the median line dorsal to the ovary. The uterus in 

 ripe proglottides is profoundly lobed, and ultimately occupies the 

 greater part of the interior of the proglottis. The cirrus and vagina 

 pass between the excretory vessels of the poral side. A unique con- 

 dition was noted in the character of the excretory vessels. On the 

 poral side the ventral vessel is the larger, while on the antiporal side 

 the dorsal vessel is the larger. This character was noted in different 



