85 
of the head, with a very slender, tube-like cavity extending* into its 
anterior end from the outside. This cavity is lined with cuticula con- 
tinuous with the cuticula covering* the head, and is thus evident!}^ 
produced by a simple invagination. The rostellum is sometimes seen 
slightly protracted, forming thus a conical tip on the anterior surface 
of the head. When retracted, the rostellum measured in two speci- 
mens 100 by 10 )~i and 100 b}^ 80 in length and width, respective!}". 
Linstow (1878b), as Grass! (18881) has remarked, erroneously described 
the rostellum of II. diminuta as a fifth sucker. 
Heel . — The neck (fig. 72) is short, 0.5 mm. (Grass!, 18881), and is 
generally somewhat smaller in diameter than the head. 
71 72 73 74 
Fig. 71.— Head and neck of H. diminuta from man. Enlarged. (After E. Parona, 1884, fig. 4.) 
Fig. 72. — Head and anterior portion of H. diminuta from rat. Enlarged. (After Zscliokke, 1889, pi. 1, 
fig. 21.) 
Fig. 73.— Head of IL diminuta. Enlarged. (After Gras.si, 18881, pi. 11, dg. 5.) 
Fig. 74. — Head of H. diminuta: ar., sucker; e.c. can., excretory canals; ros., rostellum. Enlarged. 
(After Grassi, 18881, pi. 11, fig. 2.) 
SegmenU . — The segments number 800 to 1,000 (Zscliokke, 1889), 
1,300 (Magalhaes, 1896). As in nearly all tapeworms of numerous seg- 
ments this character will be found to vary greatly. The young seg- 
ments are 20 times as wide as long. The width of mature segments 
is 15 to 20 times the length, 6 to 10 times, or even not so much as 
twice, the length. The posterior borders of the segments are only 
slightly longer than the anterior borders of the following segments, 
and the appearance of serration is thus only slightly marked. 
Genital jjores . — The genital pores (figs. 75-77, 79, 80, 82, 83, 85, 87) 
are unilateral, situated on the left side in the anterior part of each 
segment at about the junction of the anterior and middle thirds. 
Occasionally the genital pore opens on the opposite side of the seg- 
ment, but comparatively only a very few segments have the genital 
openings on the right side instead of the left. 
