132 
Heligmosomum miiris Yokogawa 
moult as in the hookworm and other forms but by the penetration of the 
larvae through the skin of the host. Entering the fifth stage the worm is 
sexually mature and is usually spoken of as the adult worm. 
(c) The First Larval Stage. 
In this stage, which extends from the hatching of the eggs to the first 
moult, the growth and development of the larvae are very remarkable. The 
changes were so great that it seemed probable that this stage must be passed 
without the lethargic stage which has been described for the larvae of other 
Strongylidae. Repeated examinations failed to show a lethargic stage so that 
the conclusion was reached that the first stage in the development of H. muris 
was passed in continuous development and activity. 
I will now describe the structure of the larvae in the first stage of develop¬ 
ment. 
Size of the larvae. The larvae (Fig. 1, Plate VII) hatched under natural con¬ 
ditions vary from 0-28 mm. to 0*30 mm. in length and from 0*015 mm. to 
0*018 mm. in thickness, measured just behind the base of the oesophagus. They 
gradually grow until the time of the first moult, when they measure from 
0*68 mm. to 0*78 mm. in length and from 0*032 mm. to 0*036 mm. in thickness. 
The larvae at this stage (Figs. 2, 3) belong to the rhabditiform type. The form 
of the body is cylindrical, decreasing in thickness from the base of the oeso¬ 
phagus to the tail. The tail is extremely slender, ending in a hair-like point. 
Body-cavity. In the larva just hatched from the egg the body-cavity is 
very small, consisting of a slight space around the digestive tract. Anteriorly 
the body-cavity is slightly expanded around the anterior part of the buccal- 
cavity and surrounds the digestive tract to the region of the anus (Fig. 2). 
Towards the end of the first larval stage this space is almost obliterated by 
the expansion of the chyle intestine. The lateral and the ventral and dorsal 
bands cannot be distinguished at this stage. 
Cuticula. The cuticula of the newly hatched larvae is very thin and without 
markings. The only change which it undergoes in the first stage is an increase 
in thickness as the size of the larva increases. 
Buccal-cavity. The buccal-cavity is quite long, having a length of 0*012 mm. 
to 0*016 mm. and is cylindrical in shape. 
Oesophagus. The oesophagus is rhabditoid in shape. The lumen appears 
as a clear line, and the “ Y-shaped mark” in the centre of the bulb is quite 
clearly visible. The walls of the oesophagus are thick and transparent, con¬ 
taining some nuclei of muscle cells and have fine transverse striations. The 
length of the oesophagus varies from 0*06 mm. to 0*146 mm. according to 
the length of the larvae (see Table I). 
Chyle intestine. The chyle intestine extends through the body from the 
oesophagus to the rectum. When observed from the side its lumen has a 
slightly irregular zigzag course. The wall of the intestine consists of two rows 
of eight cells, one row on the dorsal side and the other on the ventral side. 
