144 
Heligmosomum muris Yokogawa 
Table TV. 
1 he Size oj the Males and Females of H. muris at the beyinning 
of the Parasitic Stages. 
Age of the larvae 
Stages 
(duration after 
Length 
Width 
infection) 
Sex 
(ram.) 
(mm.) 
15 hours 
Sexes cannot 
0-68 
0-032 
First 
yet be dis- 
0-68 
0-032 
parasitic < 
stage 
Average size 
tinguished 
0-70 
0-71 
0-69 
0-028 
0-029 
0-030 
58 hours 
d 
1-43 
0-054 
60 „ 
* 
o 
1-75 
0-061 
99 99 
d 
1-29 
• 0-052 
99 99 
d 
1-28 
0-052 
Second 
joarasitic < 
Average size 
d 
1-437 
0-0547 
stage 
00 hours 
? 
1-93 
0-056 
65 
2 
1-45 
0-052 
99 99 
? 
2-08 
0-065 
99 99 - 
$ 
2-65 
0-060 
_ Average size 
$ 
2-027 
0-0582 
120 hours 
d 
4-70 
0-100 
99 99 
d 
4-52 
0-130 
99 99 
d 
3-425 
0-100 
140 „ 
d 
3-625 
0-115 
Third 
parasitic < 
Average size 
d 
4-067 
0-111 
stage 
120 hours 
$ 
4-85 
0-095 
99 9 9 
$ 
5-60 
0-125 
140 „ 
? 
6-30 
0-125 
99 99 
? 
4-63 
0-090 
Average size 
? 
5-344 
0-109 
As shown in Table IV the female 
length than the male. 
is more slender in 
proportion to the 
Shape. The changes in shape which take place during the parasitic life 
occur in the following order. At the beginning of the first parasitic stage, 
the shape does not differ to any extent from that of the mature larvae in the 
free life. They soon increase, however, much more in width than in length, so 
that the shape appears quite different from that of the mature free-living larva 
(cf. b igs. (> and 7, Plate V III). During the second parasitic stage the larvae grow 
lapidly and many characteristic changes in shape can be noted. The anterior 
end is small and the cuticular expansion, which is a differentiating character 
of the genus Heligmosomum, makes its appearance. The length of this cuticular 
expansion in the second parasitic stage is 0-025 mm. to 0-037 mm., while in 
the next stage (adult) it measures 0-06 mm. to 0-07 mm. in length. 
