Chap, xi r. ] NER vo us SYS TEM OF An THRO POD A . 



405 



(" archicerebrum" of Lan- 

 kester). Such an arrange- 

 ment is found also among 

 annulate worms. 



In the greater number 

 of the Arthropoda we 

 not only see that the nerve 

 trunks lie internally to the 

 muscular layers of the 

 body wall, but also that 

 the cerebrum is no longer 

 primitive, but has other 

 ganglionic cells used with 

 it ; or, to use the words of 

 Rathke, as applied to the 

 developing scprpion, the 

 brain is " composed of 

 several pairs of ganglia 

 lying one behind the 

 other." Nor is this kind 

 of fusion confined to the 

 brain ; a longitudinal sec- 

 tion of part of the nerve 

 cords of a crayfish shows 

 that the ganglionic cells in 

 a segment have become 

 closely united together, 

 while, at the same time, 

 the cords are still distinct. 

 Nor is this all ; while 

 Apus has a distinct gang- 

 lionic enlargement in 

 every segment of its body, 

 we find that in higher 

 forms various ganglia be- 

 come connected together, 

 until at last, in the common 



0(7 



Fig. 174 Diagram of the Ante- 

 rior Portion of the Nervous 

 System of Apus, showing the 

 " archicerebrum " (c), and the 

 Ganglia of the Lateral Cord?. 

 (From Lankester. after Zad- 

 dach.) 



x, Frontal nerves ; oc, optic nerves ; 

 CE, oesophagus ; a 1. nerve for first 

 antenna;2, nerve for serondditto : 

 Mri, nerves for mandible ; MX, for 

 maxilla; wp, for maxllliped; T 1, 

 for first thoracic appendage. 



