a STRUCTURE OF CHILOGNATHA 55 



The nervous system, in addition to the existence of the 

 visceral nerve system described by Newport, shows a marked 

 peculiarity in the form of the ventral ganglionic chain. As 

 has already been said, the nerve system consists of a brain or 

 mass of ganglia fused together and connected with the ventral 

 nervous cord by a collar of nervous substance surrounding the 

 oesophagus, and generally known as the circumoesophageal collar. 

 The ventral nerve cord is a stout cord of nervous substance 

 passing along the whole length of the animal, and situated below 

 (or ventral to) the digestive tube and the generative system. 

 This cord is enlarged at certain points, and these enlargements or 

 swellings are called ganglia, while from the ganglia pass off 

 nerves which supply the different organs of the body. In the 

 Chilognatha the cord has a compressed appearance as if the 

 ganglia were pressed into one another in such a way that it is 

 very hard to distinguish any ganglia at all. If we use the 

 microscope and examine sections cut transversely through the 

 cord, we see that it is not a simple cord. Even if we examine 

 the nerve cord with a simple lens, we see that a furrow runs 

 longitudinally down it, and the use of the compound microscope 

 shows us that this furrow represents a division into two cords in 

 such a way that the single stout cord as it appeared to the naked 

 eye is in reality two cords running side by side, and so com- 

 pressed together that the substance is partly fused together. 

 The ganglia too are double, being swellings of the two cords and 

 not a single enlargement on a single cord. As we shall see in 

 the other Orders, this arrangement constitutes a characteristic 

 distinction. 



The generative organs consist of a long tubular ovary or testis 

 lying along almost the whole length of the body and placed 

 between the digestive organ and the nervous system. Near its 

 exit from the body the long tube divides into two short tubes, 

 the oviducts in the female or the vasa deferentia in the male. 

 These ducts open in the third segment of the body, unlike 

 those of Myriapods belonging to other Orders. The accessory 

 glands present in most other Myriapods are not present in the 

 Chilognatha. 



The general arrangement of the organs of the Chilognatha 

 may be seen from Fig. 34, which represents a transverse section 

 through the body of Polyxenus (Fig. 18).. A comparison of 



