93 
In IlymenoJej^is dimiiiiitu. from man it is a very common thino- to 
find numerous sterile proglottids (figs. 87, 88). In these segments the 
female organs fail to develop properly, and no embryos are produced, 
i Such segments are readily apparent in the older portions of the stro- 
bila, reason of their clear color, due to the absence of eggs, ^yhich give 
fertile segments a somewhat dark or brownish color. These sterile 
segments have been noticed by nearly eveiyone who has ever observed 
II. diminuta from man, while in specimens from the rat they are 
much less common. Leidy (1884a), for example, gives the following 
-succession of fertile and sterile segments in a fragment about 8 cm. 
long. The fertile segments are indicated by roman type, the sterile 
by italics: 
1, 1, 6. 1, 7, 1, J, 1, IS, 1, S. 1, -i, 5, i, 1, -i, 4, 4, 1, 4, 1. 1, 5, 
T, 1, 10, 4, 6, S, 3, 13, 1, 2, 2. 
Eggs. — The eggs as first seen in the uterus do not ditfer apparently 
from the eggs as found in the ovaiy. The shell is not formed by the 
immediate action of the so-called shell gland, as might be supposed, 
during the passage of the egg through the part of the oviduct sur- 
rounded by this gland, but only becomes apparent during the progress 
of the development of the embryos in the uterus. When full}' formed 
the embryo possesses a shell in which 3 layers may be distinguished, 
an outer, a middle, and an inner (figs. 91-101). Both the embryo and 
its shell increase in size after development is begun, until the final 
stage of the eggs as they are thrown off in the feces is reached. The 
egg as seen in the feces or in the oldest segments is spherical (figs. 
91-95, 97). The outer memlrr an e is comparatively thick and delicately 
striated radialhy and is more or less yellowish in color. The inner 
memlrrane closely invests the embryo or onchosphere and is somewhat 
oval in shape, often with two polar papillae (fig. 96), as in Hymenal egri^^ 
nana, but so far as is known without filaments. This membrane is 
thinner than the outer. Between the outer and inner membranes is an 
intermediate layer of granular structure, apparently albuminous in 
character. 
When the outer envelope is broken away (fig. 99), this intermediate 
kyer remains and is seen to have a smooth external contour, as though 
limited by a very thin but distinct membrane. In sections of preserved 
material this granular intermediate layer is commonly found drawn 
away from both the outer and inner envelopes, and bounded internally 
and externally by a very delicate smooth membrane of chitinous appear- 
ance. In the granular mass are three or four or more prominent 
deeply staining nuclei. It is to the activity of these nuclei, or of the 
oells to which they belong, that the formation and growth of the shell 
of the embryo seem to be due. 
It is only in eggs of the oldest segments that the radial structure of 
the outer membrane can be distinguished; in eggs of younger seg- 
