•222 
Development oj Ascaris 
the rudiments of the muscle fields. The caudal group of nuclei which is so prominent 
a feature in the embryo is still marked. It is perforated by the rudiment of the anal 
canal leading to the rudiment of the anus. No trace of ventral gland. 
(3) Larva from the lung of the same mouse. (Mounted in Canada 
balsam.) 
Total length 0-176 mm., maximum breadth 0-016 mm., head to nerve ring 0-026 
mm., length of oesophagus 0-0.52 mm., length of oesophagus/total length 1/3-37. 
The ventral line is prominent. Rudimentary anal canal and anus distinguishable. 
A large granular eell in the posterior oesophageal region may represent the ventral 
gland. 
(4) Larva from the lung of the rat five days after the first infection 
and two days after the last. (Mounted in Canada balsam.) (PI. I, 
fig. 3.) 
Total length 0-26 mm.; head to nerve ring 0-038 mm., length of the oesophagus 
0-076 mm., length of oesophagus/total length 1/3-4. 
The nerve ring is distinet; the ventral gland is not visible; the ventral line is 
still very strongly developed; the anus is marked by a depression. 
(5) Larva from the lung of the rat six days after the first infection 
and two days after the last. (Mounted in Canada balsam.) 
Total length 0-33 mm., head to nerve ring 0-04 mm., head to end of oesophagus 
0-095 mm., length of oesophagus/total length 1/3-47. 
The three lips are clearly marked, nerve ring less so than in the earlier stages, 
ventral gland more developed and ventral line relatively less so. 
In one specimen of about this stage killed and mounted in weak corrosive sub¬ 
limate solution a prominence was noticed on the ventral side of the mouth suggestive 
of the asymmetrical boring tooth of the larvae of the ascarids of fish (Stewart, 
1914). Whether this was one of the subventral lips or a separate structure it is not 
possible to say. No such prominence is visible in specimens mounted in Canada 
balsam. 
(6) Larva from the liver of the rat five days after the first infection 
and two days after the last. (Mounted in Canada balsam.) (PI. I, 
figs. 6-7, 9-12.) 
Total length 0-375 mm., maximum breadth (opposite to the end of the oeso¬ 
phagus) 0-021 mm., head to nerve ring 0-044 mm., length of the oesophagus 0-085 
mm., length of oesophagus/total length 1/4-4. 
The head bears three well marked lips, the oesophagus is .sinuous before the 
nerve ring and is surrounded behind the nerve ring by a ring of cells which probably 
represent the collar nerve cells of free living nematodes. The ventral gland is not 
visible in this specimen. The cap of cells which overlies its anterior end can, 
however, be seen clearly in a mutilated specimen where the oesophageal region has 
been torn away from the remainder of the body. The oesophagus has retracted 
towards the head and left this group of cells clearly exposed. 
