29 
of the segment which is thus transformed into a mere egg sac. Blan- 
chard (1891a) was of the opinion that the uterus is not bounded by a 
membrane, but that the eggs lie scattered throughout the entire par- 
enchyma, so that the segment itself is, as it were, transformed into a 
uterus. That this idea is inexact, however, is readily apparent when 
one follows the development of the uterus in well-preserved material. 
As in Hymenolepis carioca the uterus is at first simply a cellular 
mass elongated transversely, lying in front of the ovary (Ransom, 
1902). This uterine primordium soon hollows out and takes on the 
appearance of a sac which rapidly fills with eggs and increases in size. 
Owing to the rapid and continued growth of the uterine wall, more 
pronounced in some places than in others, and owing to the obstacles 
by which the free expansion of the uterus is restricted, a modification 
from the condition of a simple sac-like uterus is brought about, a 
modification such as occurs in Hymenoleph carioca. and to a much 
greater degree in II. climinuta 
(p. 91). Instead of persist- 
ing as a simple sac the fully 
developed uterus has become 
a sac with infoldings, tubular 
processes, or invaginations 
extending inward among the 
eggs. 
According to Blanch- 
ard (1891a) there are about 
100 eggs in each segment; 
Mertens (1892) states 160 to 
180; Leuckart (1886a, pp. 996-997) has counted 80. From the older 
segments eggs are continually escaping through ruptures in the walls. 
Little is known with regard to the development of the eggs, but 
as first seen in the uterus they do not differ essentially in size (10 to 
15 p) and appearance from eggs which are still in the ovary. A very 
delicate enveloping membrane may at times be distinguished. The 
eoD- begins to segment soon after it enters the uterus, and embryonic 
development proceeds rapidly. The embryo increases in size and a 
definite shell is formed. 
As found in gravid segments or in the feces the egg (figs. 31-T5) 
is oval, or occasionally spherical. The shell is very clear and trans- 
parent, but may take on a slight brownish or yellowish tint after 
standing for some time in the feces (Grassi, 188Td; Calandruccio, 1890a; 
Mertens, 1892). It consists of two distinct membranes separated by an 
intervening space which contains a transparent substance, apparently 
ffuid or semi-fiuid and more or less finely granular. The outer mem- 
hrane is very thin, less than 1 p in thickness. The inner inernhrane. 
which closely invests the embryo or onchosphere as it is called, has 
Fig. 34. — Egg of T. miirina I)uj. {—H. nana). Enlarged. 
Copy of original tj-pe figure. (After Dnjardin, 184.?a, 
pi. 12, fig. A6.) 
Fig. 35. — Egg of H. nana. Enlarged. (After W. H. 
Kansom, 1856, p. 598, fig. 1.) 
Fig. 36. — Egg of H. nana. Enlarged. (After Leuckart, 
1863, p. 397, fig. 11-5.) 
