S. Yokogawa 
133 
These cells are irregular flattened, cuboidal in shape, with oval nuclei. They 
jut into the lumen of the intestine reducing it to a mere line. The cells of the 
intestinal wall vary in size, even in the same specimen, according to their 
position, viz., the cells situated at the anterior and the posterior part of the 
intestine are much smaller than those in the middle region. The protoplasm 
of these cells contains fine granules which increase in number with the growth 
of the body. Accordingly the nuclei become difficult to see in the later 
development of the first larval stage. At the boundary line between the chyle 
intestine and the oesophagus are situated four cells (Fig. 2, iv, Plate VII), 
dorsally, two on each side, which represent the primordium of the intestinal 
valves. These cells are very small and clear and each contains a round nucleus. 
Rectum. The rectum is a very fine slit-like canal lined by a thin chitinous 
membrane. Its length varies from 0-015 mm. to 0-055 mm. according to the 
length of the body. At the point where it joins the chyle intestine two to 
three small cells are visible, which seem to be the primordium of the rectal 
ligament (Fig. 2, rc). The rectum runs diagonally and is surrounded by a 
cell-group. The distance of the anus from the tip of the tail varies in the 
different sizes from 0-052 mm. to 0-11 mm. (see Table I). 
Nervous system. At the constriction of the oesophagus of the youngest larva 
of the first stage there are found a large number of round cells surrounding 
the oesophagus. The majority of these cells belong to the nervous system. 
The nerve ring appears as a band surrounded by a number of these cells 
toward the end of this stage (Fig. 4, n, Plate VII). 
Excretory apparatus. In the larvae just hatched from the eggs a number of 
round cells are found on the ventral side at the base of the oesophagus and at the 
anterior limit of the chyle intestine. This cell group is not at this stage sharply 
separated from the nerve cell group. In the last period of the first stage, two 
pear-shaped relatively large cells can be clearly seen at the same place occupied 
in the earlier stages by the cell-group mentioned above. These two cells are 
apparently separated from the nerve cell group, and are situated on the ventral 
side of the anterior part of the chyle intestine, with their narrow parts pointing 
anteriorly (Fig. 3, eg , Plate VII). In the front of these cells, a short canal is 
visible which enters into a group of cells. This canal is apparently the begin¬ 
ning of the excretory canal. The excretory pore cannot yet be distinguished. 
Genital primordium. The germ anlage is recognizable as a small elongated 
body, measuring 0-006 mm. x 0-004 mm. to 0-01 mm. x 0-06 mm., according 
to the growth of the larvae (Figs. 1, 2 and 4, gp). In the youngest larvae it 
apparently consists of two cells. It is located on the ventral side between 
the chyle intestine and the body wall near the middle body. 
Table I shows the increases in body length and in the length of certain 
other parts during the first stage of development. 
