158 
Heligmosomum muris Yokogawa 
growing forward (Fig. 24, gp, Plate XI). Toward the end of the first parasitic 
stage and especially during the second moult the female genital primordium 
increases considerably in length and begins to show differentiation (Text-fig. 7). 
At this time the subcuticular cells at the posterior portion of the body also 
increase in number. In the beginning of the second parasitic stage, the 
primordium of the ovary, seminal receptacle, uterus and the ovijector can 
be distinguished (Fig. 36, Plate XII). The oviduct is not differentiated from the 
posterior end of the ovary until the end of the second parasitic stage. During 
the first part of the second parasitic stage all of the internal sex-organs develop 
along the ventral side of the intestine, but toward the end of this stage the 
ovary increases very rapidly in length and crosses to the dorsal side of the 
intestine. As development proceeds most of the internal sex-organs grow over 
to the dorsal side of the intestine. 
The ovary. The ovary develops from the anterior part of the genital 
primordium but there is no clear separation into two regions as in the develop¬ 
ment of the testes of the male. In the first part of the second parasitic stage 
the ovary grows forward slowly along the ventral side of the intestine (Fig. 36, o, 
Plate XII), while toward the end of this stage it crosses over and develops very 
rapidly along the dorsal side of the intestine. In the first half of the second 
parasitic stage (about 58 to 80 hours after infection) the size of the ovary in¬ 
creases from 0*08 to 0-9 mm. by 0-014 to 0-12-0-14 mm. by 0-014 to 0-015 mm., 
while during the last part of this stage and especially during the last moult 
(about 85 to 108 hours after infection) it develops from 0-14 by 0-014 mm. to 
0-50-1*00 by 0-02 to 0-025 mm. In the beginning of the second parasitic stage 
the cells of the ovary are uniform in size. In the course of the second parasitic 
stage the cells in its posterior part increase in size and become arranged into 
two rows, while those of the anterior region are still small and closely packed 
(Fig. 36, o, Plate XII). During the last part of the second parasitic stage the 
ovary develops so rapidly that the wall of its posterior part comes to consist 
of flat cells, forming an empty tube. At this time the oviduct is formed from 
the posterior end of the ovary as will be explained in the following section. 
After the completion of the third ecdysis the ovary is fully developed. 
The seminal receptacle. The seminal receptacle develops from the region 
just behind the ovary. At the beginning of the second parasitic stage this 
part consists of a row of several cells which are a little larger than those of 
the uterus (Fig. 36, sr). At the end of the second parasitic stage the walls 
of the seminal receptacle consist of high columnar cells (Fig. 33, sr, Plate XII) 
having a size of about 0-10 by 0-025 mm., while the uterus and the posterior 
end of the ovary are lined by flat cells. By the time spermatozoa are intro¬ 
duced the seminal receptacle becomes a thin walled tube lined with flat cells. 
Its length in the adult worm is about 0-1 mm. and it joins the uterus without 
any sharp demarcation. 
The oviduct. The oviduct is formed chiefly from the posterior end of the 
ovary. In the last part of the second parasitic stage the walls of the posterior 
