THE DEVELOPMENT OE HELIGMOSOMUM MURIS 
YOKOGAWA, A NEMATODE FROM THE INTESTINE 
OF THE WILD RAT 1 . 
By SADAMU YOKOGAWA, M.D. 
Professor of Pathology , Medical School of Formosa. 
(With Plates VII—XII and 8 Text-figures.) 
CONTENTS. 
I. 
Introduction .... 
PAGE 
127 
11. 
The Free-living Larval Stages 
129 
1. Development of the Egg . 
129 
(a) Morphology of the Egg 
129 
(b) Formation and Hatching of 
the Embryo 
129 
2. Development of the Larvae in 
the Free-living Stage 
130 
(a) Method of Culture 
130 
(b) A General Description of the 
Stages of the Post-embry¬ 
onal Development 
130 
(c) The First Larval Stage 
132 
(d) The First Moult . 
134 
(e) The Second Larval Stage (the 
Infective Stage) 
135 
3. The Influence of the Environ¬ 
ment on the Eggs and Larvae 
138 
(a) Air ..... 
138 
( b) Light ..... 
138 
(c) Moisture .... 
139 
( d) Temperature 
139 
III. 
Method of Infection and Migra¬ 
tion in the Host . 
139 
1. Infection through the Mouth 
139 
2. Infection through the Skin 
140 
IV. 
Parasitic Stages 
140 
1. Outline of Parasitic Develop¬ 
ment ..... 
140 
(a) General Considerations 
140 
(6) The First Parasitic Stage or 
the Third Larval Stage 
141 
PAGE 
(c) The Second Moult . . 141 
(d) The Second Parasitic Stage 
or the Fourth Larval Stage 143 
(e) The Third Moult . . . 143 
(/ ) The Third Parasitic or Adult 
Stage . . . .143 
2. Special Description of the De¬ 
velopmental Changes during 
the Parasitic Stages . . 143 
(a) Size, Shape and Colour. . 143 
( b) The Cuticula . . . 145 
(c) Digestive System . . 146 
( d ) The Excretory System . 147 
3. Sexual Differentiation and the 
Development of the Repro¬ 
ductive Organs . . .148 
(a) General Discussion . . 148 
(b) The Beginning of Sexual 
Dimorphism . . . 149 
(c) The Development of the 
Male Reproductive Organs . 152 
(1) The Internal Sex-Organs. 152 
(2) The External Sex-Organs 156 
( d ) The Development of the Fe¬ 
male Reproductive Organs . 157 
(1) The Internal Sex-Organs. 157 
(2) The External Sex-Organs 161 
V. Adult.162 
VI. Summary ..... 163 
References . . . .165 
Description of Plates . . 165 
I. INTRODUCTION. 
The post-embryonic development of nematodes is very insufficiently known. 
A surprisingly small number of forms have been studied and in many of these 
investigations the work is entirely inadequate. Leuckart (1887) investigated 
1 This paper is a contribution from the Department of Medical Zoology of the School of Hygiene 
and Public Health of the Johns Hopkins University. 
