142 
Heligmosomum muris Yokogciwa 
uncommon to see a larva carrying around the old skin out of which it has 
partly wriggled. When they cast the old cuticula 'they become very active 
and soon after start their migration toward the intestine of the host. The 
larvae which are found in the lungs are always in the first parasitic stage or 
in the moult, while in the intestine some will be found in the second parasitic 
stage. 
Text-fig. 3. Larvae during the first parasitic stage in the lungs of an experiment rat, 
35 hours after infection, a, Male; b, female. 
The structural changes which occur during the moulting process are as 
follows: 
(1) ihe buccal-cavity loses its cylindrical shape and becomes greatly 
reduced in size. 
(2) Hie oesophagus extends almost up to the anterior end of the body. 
(3) The characteristic cuticular expansion arises at the anterior end of the 
body. 
