358 BIOLOGY. 



highest arteries, however, are the air- tubes. The nerves 

 therefore run parallel with the tracheal systems, 



2019. What the tracheae are for the vegetative body, 

 namely, the vitalizing and motor principle, such are the 

 nerves for both the animal and vegetative body. 



2020. The nerves are distributed like the tracheae of 

 plants, in individual threads or filaments, which run near 

 to each other arranged in a fascicular manner, and then 

 mutually separate. 



2021. The nervous filaments everywhere accompany 

 the arteries, and, as far as their ultimate ramifications, like 

 the tracheae of insects pass to all parts of the body. 



2022. The nervous mass has been separated into an 

 arteriose and venous mass, the former being the cineritious 

 or gray substance, the latter the medullary or white. The 

 nervous system is therefore an entire blood-system, with 

 two poles; it is therefore alive and active for itself, or 

 independent of other systems. 



2023. Both nervous masses are in a state of constant 

 tension against each other, and consequently in constant 

 tension with the whole body. 



2024. The nerves are filaments that, upon the separa- 

 tion of the parts of the body, have remained behind, just 

 like the arteries are tubes individualized in the general 

 parenchyma, throughout which the sap was previously 

 dispersed as in the vegetable trunk. The first indivi- 

 dualization necessarily takes place at the oral extremity. 

 The first nerve is a ring, surrounding the oesophagus 

 or gullet. Thus, if the body consists of several con- 

 secutive rings or cysts, as in the Worms, each ring 

 will or can have its nervous ring, which inferiorly 

 gives off nerves to the vegetative organs, and superiorly 



* , to the animal, if these be present. Such a point for 

 J*** 1 gi vm g on nerves is called a ganglion ; since also every 

 rf> <>4 ganglion sends off nerves to join other ganglia ; so both 

 below and above a nervous cord or string will originate 

 in the longitudinal direction. The nerves, which have 

 been left behind in the vegetative parts, form the vege- 

 tative nervous system ; those that remain in the animal 

 parts, the animal system. 



