32 
hooks with which the onchosphere is supplied are usuallv found 
directed toward one pole (Mertens, 1892; Miura & Yamazaki, lS9T,and 
others), and as has been pointed out in other tapeworms (Siebold, ISod; 
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 /i. Leuckart (1863, 1886a, p. 996) found them 10 to 58 yw. 
Grassi (18T9h), 33 by 33 and 33 to 36 by 28 to 31 yw. Grassi & Cal- 
andruccio (1887a) 13 by 35 yw to. 53 by 10 yu. Perroncito & Airoldi 
(1888a, b, c), outer membrane, 10 by 32 yw to 52 Iw 
11 /u inner membrane, 21 bv 20 ju to 31 by 21 ju. 
Mertens (1892), outer membrane, 33 by 39 yu to 15 
by 60 yu; inner membrane, 26 by 25 yu to 30 b}^ 29 
yU. Senna (1889), 10 by 36 to 50 by 10 /<. Lin- 
stow (1896a), outer membrane, 39 by 39 yw and 13 
by 31 yw; inner membrane, 28 by 28 yu. Blanchard 
(1891a), outer membrane, 30 to 37 p. by 18 to 55 p\ 
inner membrane, 16 to 19 p. According to my own 
measurements the outer membrane rang'es from 36 
by 32 p to 56 by 12 p\ the inner membrane from 
18 by 20 p to 21 by 32 p. The onchosphere is 5 to 
10 p smaller than the inner membrane. The size 
of the einbryonal hooks has been given by various authors from 9 to 16 
p\ according to Blanchard (1891a), with whose figures mine agree, 
they measure 10 to 12 p. From measurements of 9 eggs, Miura & 
Yamazaki (1897) give the following' figures: 
Outer envelope — Length: Maximum, 56.7 p\ minimum, 11.3 p; 
mean, 50.7 p. Breadth: ^Maximum, 53.2 yu; minimum, 35.1 yw;_ mean, 
12.9 p. 
Inner envelope — Length: Maximum, 32.1 yw; minimum 27 p\ mean, 
30.1 p. Breadth: Maximum, 29.7 p: minimum, 21.3 yw; mean, 25.9 p. 
Hooks of embryo — Maximum, 13.5 p: minimum, 10.8 p\ mean, 
12.9 p. 
As to the eggs of Ilyrnenoleyois nana from the rat, which some 
authors have considered larger than those of the form found in man, 
it may be said, in the first place, that the size of the eggs is a very 
variable character as the figures already given testify, and it is conse- 
quently doubtful if a satisfactory comparison could be instituted or 
any constant difierence be discovered between the two forms in this 
regard; and in the second place, considering the great variability 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 generalH, larger or 
smaller in one case than in the other. Dujardin (1815a) gives the size 
Fig. 45. — Egg of H. nana, 
as seen in fresh feces. 
Enlarged. (After Ran- 
som, from Stiles, 1903a, 
p. 85, fig. 85.) 
