192 
Development of Ascaris 
jects into the anterior end of the intestine. The external surface of 
the oesophagus is, as in the adult, covered with a sharply staining 
cuticle, a structure which is acquired in the passage along the alimentary 
canal of the rodent since it is not present in specimens from the trachea 
or mouth. In correspondence with the formation of this cuticular coat 
is the reduction of the cellular investment of the oesophagus, which is 
at its greatest development on the 5th or 6th day after infection. 
The body of the oesophagus is distinctly muscular. 
The intestine is patent and is composed of a tesselated cylinder of 
hexagonal cells (PI. IV, fig. 5). The anal canal is curved, expanded at 
the anterior extremity, and lined with cuticle. 
The nerve ring is large and obvious (Figs. 2, 9) and possesses a 
cellular sheath. It lies immediately in front of the excretory aperture. 
An anal ganglion is formed by the ingrowth of the dorsal and lateral 
lines (Fig. 8). 
The body of the unicellular excretory gland lies mainly between 
the left lateral line and the oesophagus (Figs. 2, 3, 4, 6, 10); a process 
however extends across the body and comes into contact with the 
right lateral line (Fig. 10). Its anterior extremity also passes toward 
the ventral line and meets the group of cells which contain the anterior 
portion of its duct. A considerable portion of the cell is occupied by 
the nucleus which is furnished with six chromatin masses of varying 
size. The excretory pore is situated in the ventral line immediately 
behind the nerve ring. From it the excretory duct (Figs. 2, 3, 4) passes 
backward through the group of cells of the ventral line referred to above 
(Figs. 2, 4), inclines to the left and enters the body of the gland in the 
left lateral line. It does not send a branch toward the right lateral line. 
In younger larvae of 1 mm. or less in length the excretory gland 
appears to be confined to the left side of the body and not to send a 
process to the right lateral line. It is however also in contact with the 
ventral line and it appears probable that it originates from the ventral 
line and is homologous with the ventral gland of free-living nematodes. 
It is interesting to observe the manner in which the left-sided gland of 
the larva under consideration fits into the scheme of evolution of the 
excretory organ of nematodes as worked out by Jaegerskioeld (Jaeger- 
skioeld, ‘Beitr. zur Kennt. der Nematoden,’ Zool. Jahrb. Anat. Ontog. 
vii. 449; Stewart, Quart. Journ. Micr. Sci., l. 141). The unilateral 
organ of the younger larvae corresponds with that of Ascaris decipiens, 
the unequally bilateral organ of the older larvae with that of A. rotundata. 
The rudiment of the gonads is situated about the junction of the 
