NEMATODA 127 
off transverse branches, which unite, and open by a minute 
pore in the ventral middle line. The canals end blindly, their 
walls consist of a granular protoplasm containing nuclei con- 
tinuous with the subcuticular protoplasmic layer, and of an 
internal refractive layer. They contain a fluid. 
The granular layer of protoplasm which hes between the 
cuticle and the longitudinal muscles is also heaped up in the 
middle dorsal and ventral lines, thus forming a ridge sur- 
rounding the dorsal and ventral nerves. This separates the 
dorsal and ventral longitudinal muscles into two lateral halves. 
The nervous system consists of a ring surrounding the 
oesophagus, which may be swollen into an inconspicuous 
ganglion on the ventral side. The ring gives off anteriorly six 
short nerves which run towards the head; of these two are 
lateral and run in the lateral line, and the other four are 
arranged symmetrically, one each side of the dorsal, and one 
each side of the ventral middle line. ‘The ring gives off 
posteriorly a dorsal and ventral median nerve, the chief 
nerves in the body. The ventral nerve stops in front of the 
anus, where it bears a ganglion. The dorsal and ventral 
nerves are connected at intervals by lateral commissures, 
which usually arise alternately. Probably four smaller nerves 
also pass backward from the oesophageal ring, lying in the 
same lines as the four small nerves which run to the head. 
The nerves all lie in the granular protoplasm surrounded by 
the longitudinal muscles. 
The sexes are separate. The male reproductive organs lie in 
the hinder third of the body (Fig. 81). The testis is single, and 
consists of a long tube which winds about in the body-cavity, 
and at its lower end opens into the long vesicula seminalis. 
The testis is lined with a layer of nucleated protoplasm. The 
mother cells of the spermatozoa arise from a central rachis ; 
when they break off from this they divide into two and then 
into four, each quarter then becomes a spermatozoon. Whilst 
in the body of the male, the spermatozoa have a rounded out- 
line, but when introduced into the female they exhibit 
amoeboid movements. This peculiarity, together with the 
absence of any tail to the spermatozoa, is characteristic of the 
group of Nematodes. 
