140 
Heligmosomum muris Yokogawa 
(c) Digestive System. 
The mouth and buccal-cavity. The buccal-cavity of the larva in the first 
parasitic stage becomes shorter and wider than that of the mature, free- 
living larva. The anterior end of the larva at this stage becomes wider and 
blunter and the prominent edge of the mouth, which was recognizable in the 
earlier stage, disappears. With the increase in size of the anterior end the 
mouth expands more rapidly than the buccal-cavity, making this cavity funnel- 
shaped. The length of the buccal cavity of the larvae in the first parasitic 
stage is 0-005 mm. to 0-008 mm., while in the mature free-living larvae it 
had a length of 0-009 mm. to 0-019 mm. 
After the completion of the second ecdysis, the buccal-cavity is almost 
obliterated by the forward growth of the oesophagus, only a very small space 
being left. 
After the disappearance of the larval buccal-cavity, the mouth cavity of 
the adult stage is found at the anterior end of the body, surrounded by the 
inflated cuticula and the subcuticular layer (Text-fig. 1 b). 
Oesophagus. The oesophagus of the larvae in the parasitic life is conoidi- 
form and its length can be modified in an individual worm by contraction 
of the body. At the beginning of the first parasitic stage it measures about 
0*17 mm. to 0-19 mm. in length, while it is about 0-27 mm. to 0-32 mm. long 
at the beginning of the next stage. After the completion of the third ecdysis, 
the oesophagus measures from 0-35 mm. to 0-45 mm. in length. 
Oesophageal glands. After infection, the granular strands which represent 
the substance of the oesophageal glands increase in number as described by 
Looss (1905, pp. 88 and 89) for the hookworm, and the sub ventral gland-cells 
become hard to see, being covered with the granules, while there can be seen 
a large vesicular ovoid nucleus at the dorsal side of the posterior end of the 
oesophagus (Fig. 7, eg, Plate VIII). 
Intestine. There are remarkable changes in structure of the intestine of 
the larvae soon after the beginning of parasitic life. The cells of the intestinal 
wall become greatly thickened, become loaded with pigmented granules, and 
also increase in number (Fig. 7, Plate VIII and Text-fig. 3 a and b). I found in 
one specimen from the lungs of an experimental rat 15 hours after infection that 
one side of the intestine consisted of twelve cells, while the other side was 
composed of fourteen cells. It is evident that the cells divide as development 
proceeds since a greater number of cells are found in the intestinal wall of 
the larvae in more advanced stages. The intestinal cells of the larvae in the 
parasitic life are so dark and crowded with granules that it is difficult to see 
the nuclei. At the anterior limit of the intestine there are found in the parasitic 
stages the small clear cells which are the cells of the intestinal valve, which 
were present in this region in the free-living larvae. 
Rectum. The morphological changes in the rectum of the larvae during 
the parasitic stages of development are very great and differ in the two sexes. 
