NE MA TO DA 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 lies 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 

 alsp 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 seminahs. 

 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. 



