Some J'ariatioits in Hymcnolcpis diminuta 7 



form, are placed more or less anteriad and measure from 80 to 

 160 /I. in diameter, in this specimen only 86 /x, close to the mini- 

 mum. A small rostellum without hooks is found at the anterior 

 point of the scolex. It is slightly retractile and may be withdrawn 

 inward, leaving a shallow pocket or hollow at the anterior tip. 

 On the other hand, it may be protruded, giving the head a 

 bluntly pointed appearance. The rostellum is a pyriform muscu- 

 lar sac with an outer layer of longitudinal and an internal of cir- 

 cular fibers. The large end is anteriad ; it is surrounded by the 

 parenchyma of the scolex. According to Ransom, when retracted 

 the anterior portion is invaginated, forming a tube-like cavity ex- 

 tending inward from the anterior surface of the scolex into the 

 middle of the rostellum and lined with cuticula continuous with 

 that of the external surface of the parasite. This is best seen in 

 the living worm. In this long specimen the rostellum shows noth- 

 ing more than a shallow depression anteriad. The excretory 

 vessels within the rostellum described by Ransom as consisting of 

 two loops here have the appearance of an irregular network or 

 system of lacunae. 



The shape of the rostellum is not strictly pyriform in this speci- 

 men, since there are four somewhat concave surfaces correspond- 

 ing to the proximity of the four spherical suckers. It measures 

 39 ju, in width at about 30 /i. from the anterior end, and runs 

 throughout the eleven sections of 10 /t each. The thickness in 

 this case is apparently greater, due probably to a slightly oblique 

 section. These measurements were made from sections. In al- 

 most all of my scolices mounted in toto the rostellum has a length 

 of 93 /x with a Avidth usually of 53 /x, in the lowest case 40 /x. 

 The neck is always short, as Grassi gives it at 0.5 mm. It may 

 equal- or exceed in width the scolex, as is shown in figures 2 and 

 II. but is generally not so wide (figs, i, 12). 



The greatest number of proglottides yet given for this form is 

 1,300 by Magalhaes. My specimen by actual count possesses 

 over 2,850. The youngest proglottides are 23 ix by 270 fx, eleven 

 times as wide as long. Twenty cm. from the scolex in toto 

 mounts they measure 240 ju, by 1,650 fx or nearly seven times as 

 wide as long. At 40 cm. from the scolex they measure 300 /a by 



141 



