150 
♦ 
Heligmosomum muris Yokogawa 
In the first larval stage, the genital primordium is located at about the 
middle of the body. After the completion of the first moult, its position is a 
little behind the middle part of the body on account of the relative reduction 
in the length of the posterior part of the body, and the considerable increase 
in the length of the oesophagus (see Table II). 
Table V shows the backward shifting of the position of the genital pri¬ 
mordium during free life. 
Table V. 
The Position of Genital Primordium during Free Life. 
Body 
Body 
Size of germ 
Position of germ 
Percent, of 
Stages in 
(length) 
(width) 
cell group 
cell group (dist. 
distance from 
free life 
(mm.) 
(mm.) 
(mm.) 
from ant. end) 
anterior end 
f 0-280 
0-015 
0-006 x 0-004 
0-148 
52-8 
First larval stacm 
< 
0-300 
0-018 
0-006 x 0-004 
0-153 
51-2 
© 
0-395 
0-018 
0-007 x 0-004 
0-202 
51-3 
_ 0-442 
0-022 
0-007 x 0-004 
0-235 
53-2 
r 0-660 
0-034 
0-010x0-005 
0-330 
50-0 
0-680 
0-032 
0-008 x 0-005 
0-340 
50-0 
First moult 
■< 
0-700 
0-033 
0-010 x 0-006 
0-376 
53-0 
0-720 
0-034 
0-010 x 0-005 
0-387 
53-7 
0-750 
0-034 
0-012 x 0-006 
0-387 
51-6 
[ 0-680 
0-028 
0-016 x 0-008 
0-390 
57-3 
Second larval stage 
0-715 
0-026 
0-016 x 0-007 
0-420 
58-7 
(the mature free- 
J 
A 
0-740 
0-026 
0-017 x 0-008 
0-435 
58-7 
living larvae) 
0-630 
0-025 
0-012 x 0-008 
0-382 
60-6 
0-715 
0-025 
0-014 x 0-008 
0-420 
58-7 
As shown in 
Table V 
the genital primordium of the mature free-living 
larvae is situated near the middle body and no differences in its position can 
be noted between the sexes. After infection a remarkable differentiation of 
position of the genital primordium in the sexes comes about. Examining many 
specimens in parasitic stages, I found that the genital primordium of the 
female migrates from near the middle of the body toward ^ts posterior end, 
while that of the male does not migrate but remains near the middle of the 
body. This remarkable migration of the genital primordium of the female 
takes place between 20 to 30 hours after infection. By 30 hours after infection 
the genital primordium of the female has reached a position just in front of 
the anus (Text-fig. 3 h). Table IV shows the progress in this migration com¬ 
paring the position of the genital primordium in both sexes at various times 
after infection. 
hrom Table VI it can be seen that as early as from 24 to 30 hours after 
infection the males and females are differentiated bv the position of the genital 
primordium. 
Finding many varying shapes of the tail of the mature free-living larvae 
(Text-fig. 4) I tried in vain to establish a sexual dimorphism in this character. 
I finally came to the conclusion that these differences were nothing but indi- 
# o 
vidual variation. I found, however, structural differences between the posterior 
ends of the sexes very early in the parasitic development. The posterior end 
