8. Yokogawa 
(d) The Second Parasitic Stage or the Fourth Larval Stage. 
The larvae in the second parasitic stage (fourth larval stage) always reach 
the intestine of the experimental rats soon after the casting of the old cuticula. 
Usually they travel from the lungs to the intestine about 50 to 60 hours after 
infection. Sometimes they are found in the intestine as early as 45 hours 
after infection, while in some cases they remain in the lungs undergoing 
moulting as long as 72 hours after infection. The growth of the larvae during 
this stage is very rapid, and they soon start the third ecdysis and reach the 
adult stage. It is during this stage that the sexual organs develop with 
remarkable rapidity as will be described in a later section. 
(e) The Third Moult. 
The third moult usually begins from 90 to 108 hours after infection and 
lasts for about 12 to 15 hours. The larvae in the moult are found somewhat 
coiled. The structural changes which occur during the third moult are as 
follows: 
(1) The newly formed cuticula is provided with prominent longitudinal 
markings in the form of ten ridges. 
(2) The reproductive organs become fully formed. 
(/) The Third Parasitic or Adult Stage. 
Shortly after completion of the third ecdysis, the larvae reach sexual 
maturity. The mechanism of the casting of the cuticula does not differ from 
that of the previous moult. The ecdysis of the female occurs a little later than 
that of the male. The structure of the adult worm will not be included in 
this paper, because it has been described in my previous paper (Yokogawa, 
1920). During this stage there are two layers of the cuticula, the outer ap¬ 
parently representing the fourth moult, but never being shed. 
2. Special Description of the Developmental Changes 
during the Parasitic Stages. 
(a) Size, Shape and Colour. 
• 
Size. The larva, after penetration into the host, increases very rapidly 
in size. At the beginning of the first parasitic stage the increase in width is 
especially marked while the increase in length is greatest during the later 
stages. After the sexes are differentiated the female is almost always larger 
than the male. The moults of the females in the parasitic stages come a little 
later than those of the males. Table I\ indicates the size of both sexes at 
the beginning of the parasitic stages. 
