8. Yokogawa 
141 
From the morphological and biological view point, the parasitic life of this 
species can be divided into three stages, viz., the third larval stage, or the 
first parasitic stage; the fourth larval stage, or the second parasitic stage; 
and the stage of the adult worm, or the third parasitic stage. These stages 
are separated by two moults. On account of the great complication of the 
parasitic development I will first give a general outline of the changes which 
go on, and will then describe in detail the development of certain of the organs. 
(b) The First Parasitic Stage or the Third Larval Stage. 
The first parasitic stage of H. muris begins at the moment of penetration 
of the mature larvae into the host and is divided from the second parasitic 
stage (fourth larval stage) by the second ecdysis. This stage is not separated 
from the second larval stage by a moult but is differentiated from it by a 
complete change of environment which initiates profound morphological 
changes. The larvae after penetrating r into the host are found first in the lungs 
of the host in about 14 to 20 hours. Usually they remain for about 35 to 50 
hours in the lungs since they are found in this location until 50 to 65 hours 
after infection. Exceptionally, larvae were found in the lungs of the host 
72 hours after infection. Toward the end of their sojourn in the lungs the second 
moult begins. 
The structural changes which take place during the first parasitic stage 
may be summarized as follows (Fig. 7, Plate VIII and Text-fig. 3 a and b): 
(1) The larvae grow rapidly, increasing more in width than in length. 
(2) The buccal-cavity becomes shorter and wider. 
(3) The oesophagus increases in length. 
(4) The cells of the intestinal wall increase in thickness and in number. 
They come to contain so much pigment that their nuclei cannot always be 
detected. 
(5) The excretory system becomes clearly differentiated. The cervical 
glands are now seen dorsally in the body-cavity at the anterior region of the 
intestine, and the excretory pore can be distinguished on the ventral surface 
in the oesophageal region. 
(6) The differentiation of the sexes occurs during this stage. 
(c) The Second Moult. 
The second moult occurs usually toward the end of the life in the lungs. 
The preparation for this moult begins from 35 to 40 hours after infection, and 
the process of moulting extends over a period of from 12 to 15 hours. The 
larvae at the time of moulting move very slowly and become somewhat coiled. 
In observing some larvae in the process of moulting, I noticed that a longitudinal 
rupture of the old cuticula occurred at the base of the oesophagus. Through 
this opening the larva gradually worked its way sideways, withdrawing the 
anterior end from the anterior region of the cuticula and in so doing in- 
vaginating the cuticula of this region like the finger of a glove. It is not 
