83 
of the egg of mnrina {— IL nami) from the rat as 65 Linstow 
(1866a). 46 by 42 f.i to 54 hy 47 yw; measurements which I have made 
range from 36 l)v 26 ii to 52 by 36 yw. With the exception of Dujar- 
diivs figures these sizes fall within the limits established for Tli/meiu)- 
Ipph nana from man. 
Senna (1889) noticed in feces containing completely developed eggs 
of ITynienoleph nana, in six cases, numerous small rounded bodies 
(tig. 43) measuring from 5 to 10 p to 30 p in diameter. The smaller 
of these were hoinogeneous in appearance, tinted like mother-of-pearl, 
and 1)ounded by a very thin membrane, while the larger were more 
granular and tended to beconu' oval, with a thicker membrane, as indi- 
cated by a distinct!}^ double contour. Senna was inclined to interpret 
these as eggs in course of development, which had prematurely escaped 
from the uterus, but since he found similar bodies in two cases in 
which he could not demonstrate the presence of TL he was left 
in doubt with regard to their nature and significance. 
])KA'KLOFMKNT AND LIFE HISTORY. 
The Avell known and usual mode of development of tapeworms of 
the family Tjeniidie, to which Ilymenolepis nana belongs, is as follows: 
The eipp containing ^ie-Jioolced embryos pass out of the body of the 
definitive host in the feces. To develop further they must be taken 
into the alimentary canal of some other animal. If the conditions are 
suitable in this animal the embryos, after hatching, if this has not 
already taken place, l)ore out of the alimentary canal, and, enc 3 ^sted 
somewhere in the tissues of the body, develop into the intermediate 
stage, cystwereiis or cysticercokl^ as the case may he. When this ani- 
mal, the intermediate host, is eaten b}- an animal which can act as a 
definitive host, the intermediate stage continues its development and 
becomes transformed into the adult which produces eggs, thus 
completing the cvcle. As one would expect, the normal intermediate 
host is an animal which is the natural food of the definitive host, or 
otherwise likely to be taken into the alimentary canal of the latter. 
Leuckart (1863, pj). 395,397), upon theoretical grounds, assum- 
ing that an interchange of hosts occurred during the life histoiy of 
Jlymeholepk uaua and noticing the great similarity in the anatomical 
characters of the Avorm in (piestioii, of certain tapeworms from mice 
and shrew-mice and of a cvsticercoid found Iw Stein in the meal worm," 
expressed the opinion that the intermediate stage Avas deA^eloped in 
some insect. ^ 
" Hooks very similar in form are found in the related tapeworms of our mice and 
shrew-mice, as well as in the cvsticercoid of Stein from the meal worm. (Trans- 
lation of Leuckart, 1863, j). S9b . ) 
We content ourselves * * * with the supposition that, as in the most nearly 
related species, the worm passes its youth as a cvsticercoid in some insect. (Trans- 
lation of Leuckart, 1863, j). 397. ) 
19203— No. 18—04 3 
