32 
hooks with which the onchosphere is supplied are usually found 
directed toward one pole (Mertens, 1892; Miura & Yamazaki, 1897, and 
others), and as has been pointed out in other tapeworms (Siebold, 1851; 
Ransom, 1900), the middle pair differ from the other by being more 
slender and without a definite ventral root. 
Various sizes have been assigned to the eggs, and there is, in fact, 
considerable actual variation. Bilharz (Siebold, 1852) gives a diameter 
of 26 /^. Leuckart (1863, 1886a, p. 996) found them 10 to 58 pi. 
Grassi (18T9h), 33 by 33 yu and 33 to 36 by 28 to 31 pi. Grassi & Cal- ! 
andruccio (1887a) 13 by 35 pi to 53 by 10 j~i. Perroncito & Airoldi i 
(1888a, b, c), outer membrane, 10 by 32 yw to 52 by I 
11 yu; inner membrane, 21 by 20 pi to 31 by 21 pi. 
Mertens (1892), outer membrane, 33 by 39 yu to 15 | 
by 60 yu; inner membrane, 26 by 25 pi to 30 by 29 i 
pi. Senna (1889), 10 by 36 pi to 50 by 10 pi. Lin- | 
stow (1896a), outer membrane, 39 by 39 pi and 13 j 
b}" 31 yw; inner membrane, 28 by 28 pi. Blanchard 
(1891a), outer membrane, 30 to 37 pi by 18 to 55 pi\ 
inner membrane, 16 to 19 pi. According to my own 
measurements the outer membrane ranges from 36 
by 32 pi to 56 by 12 yu; the inner membrane from 
18 Iw 20 pi to 21 by 32 pi. The onchosphere is 5 to 
10 fi smaller than the inner membrane. The size 
of the emljryonal hooks has been given by A^arious authors from 9 to 16 
pi\ according to Blanchard (1891a), Avith whose figures mine agree, 
theA" measure 10 to 12 pi. From measurements of 9 eggs, Miiira & 
Yamazaki (1897) gAe the following figures: | 
Outer euA^elope — Length: Maximum, 56.7 yw; minimum, 11.3 yw; | 
mean, 5t).7 pi. Breadth: ^Maximum, 53.2 yw; minimum, 35.1 yu; mean, ; 
12.9 pi. I 
Inner eiiA'elope — Length: Maximum, 32.1 yw: minimum 27 /^; mean, 
30.1 pi. Breadth: Maximum, 29.7 yw; minimum, 21.3 yu; mean, 25.9 pi. ! 
Hooks of embiyo — Maximum, 13.5 yw; minimum, 10.8 yu; mean, 
12.9 pi. I 
As to the eggs of Ilymenolepis nana from the rat, which some . 
authors have considered larger than those of the form found in man, ' 
it maA" be said, in the first place, that the size of the eggs is a A^ery i 
Available character as the figures already giA’en testify, and it is conse- 
quently doubtful if a satisfactory comparison could be instituted or J 
aiiA" constant difference be discoA’ered between the tAvo forms in this • 
regard; and in the second place, considering the great Availability of 
this character, that it would be necessary to make measurements of a ^ 
large number of examples, with due regard to similarity of conditions, 
etc., before one affirmed that the eggs were, even generally, larger or 
smaller in one case than in the other. Dujardin (1815a) giA^es the size 
Fig. 45. — Egg of H. nana, 
as seen in fresh feces. 
Enlarged. (After Ran- 
som, from Stiles, 1903a, 
p. 85, fig. 85.) 
