NEW SPECIES OF HYMENOLEPIS 



237 



very variable in shape and size. It may present a spherical, truncate- 

 conical or cordate shape, measuring o. 1 7-0.21 mm. in both length and 

 greatest breadth. The rostellum in the protruded state may be 0.11 

 mm. long and 0.05 mm. broad. It is sometimes found retracted 

 into the rostellum-sac (fig. 4). Its armature consists of a single 

 circle of hooks, io in number and each 0.03-0.05 mm. long (fig. 3). 

 The suckers are of an oval shape, measuring 0.07-0.12 min. by 0.06- 

 0.09 mm. The neck is but little marked in contracted specimens ; 

 even in the extended state it is short, measuring o.I-0.2tnm. in 

 length by a breadth of 0.05-O.07 mm. 



The genital pores are all unilaterally situated. In each segment the 

 pore opens at about the middle of the anterior half of the lateral margin. 



Male reproductive organs. — The cirrus pouch (figs. 6, 8 & IO, cp) 

 is long and nearly cylindrical, being somewhat thicker in the proximal 

 than in the distal parts. Length about 0.3 mm. ; greatest thickness 

 0.02-0.027 mm. From the genital cloaca it runs transversely, passing 

 both the dorsal and ventral excretory vessels of the porose side on 

 the dorsal side, and reaching with its inner end the level of the excretory 

 vessels of the aporose side. In its course the pouch is gently bent so 

 as to present concavity on the ventral side. The wall is seen to be 

 made up of longitudinal or more or less obliquely running muscular 

 bundles measuring 0.0075 mm. in thickness. They are closely set 

 together in young segments, but in the older segments they leave 

 distinct spaces between them (fig. 7). 



The slender cirrus is armed with minute spines. It is often found 

 externally protruded from the genital opening (fig. 6, c). 



The vas deferens is short and thin (0.004 mm. thick). It connects 

 the inner end of cirrus pouch with the seminal vesicle, which is 

 situated directly dorsal to the former. The seminal vesicle is ovoid 

 or spherical, 0.02-0.037 mm - m diameter, looking very much like a 

 testis. It occurs even in the last segments in which the testes have 

 atrophied (figs. 8 & 10, sv). 



