F. H. Stewart 
191 
The anatomy of larval Ascaris lumbricoides L. (A. suilla Duj.) from 
the large intestine and faeces of the mouse between the 10 th and 15 th days 
after infection. 
The general shape (PI. IV, fig. 1) is cylindrical, tapering slightly to 
the truncated head, sharply to the pointed tail. The head (Fig. 3) 
bears the three mamilliform lips characteristic of the genus. The shape 
of the tail is well shown in Fig. 11. The tip is curved toward the dorsum. 
The resemblance of this outline to the figures given by Leuckart of the 
tails of a young Ascaris lumbricoides (85 mm.) from man (Menschl. 
Parasiten, n. pt. 1, p. 217) and of young A. mystax from the dog (ibid., 
pt. 2, p. 283) is worthy of note. 
The cuticle is not ringed. In sections a fine sharply-marked and 
densely-staining outer membrane can be distinguished (PI. IV, figs. 6, 7, 8) 
which is not present in the larvae found in the trachea or mouth (Figs. 9, 
10 ) and is doubtless formed by reaction to the gastric and intestinal 
juices. Lateral membranes are present extending from the head to 
behind the anus (Figs. 6, 7, 8, 9, 10). These structures are first formed 
when the larvae are passing through the bronchi and trachea and have 
attained to a length of one millimetre. In a specimen measuring 1-5 mm. 
from the mouth, the membrane extends from the nerve-ring to the anus. 
The process of development of the membrane can be made clear by 
comparison of sections of larvae from the trachea and caecum. In the 
former the cuticle is raised along the lateral lines enclosing a space, 
triangular in cross section, the base of which is formed by the lateral 
lines. The cuticle forming each side of this triangle contains a slightly 
thickened and strongly staining lamina. The unspecialised and feebly 
staining cuticle of the body surfaces passes over the outer surface of 
these laminae. In the larvae from the caecum and faeces the laminae 
have become more thick and rigid and have partially coalesced, pro¬ 
ducing a sharp keel-like ridge with a flat base. The lateral membranes 
are curved toward the dorsum. Lateral membranes do not of course 
occur in the adult. They are doubtless formed to assist in the active 
swimming movements of the larvae. 
Longitudinal lines. The lateral lines contain as a rule three nuclei 
in a cross section, dorsal and ventral lines one or two. 
Muscle-fields. If the sections are counterstained with eosine the 
muscle cells can be seen to have assumed the folded form characteristic 
of the majority of adult nematodes. 
The oesophagus (PI. IV, figs. 2, 3) is club-shaped, anterior extremity 
slightly thickened, posterior extremity markedly so. The latter pro- 
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