256 



FUNCTIONS OF THE NERVOUS SYSTEM. 



Fig. 126. 



Nervous System of Larva of Sphinx ligus- 

 tri, after Newport; A, cephalic ganglia; 1-11, 

 ganglia of tlie trunk, disposed at nearly equal 

 distances ; the last is formed by the consoli- 

 dation of the llth and lt>th. 



are the nutritive functions among the Mol- 

 lusca. Accordingly, we rind the deve- 

 lopment of the Nervous system to bear a 

 special reference to them ; and the sensori- 

 motor divisions of it can be more distinctly 

 separated, than in the Mollusca, from the 

 portion which ministers to the organic func- 

 tions. 



325. The general arrangement of the 

 Nervous System differs so little, except as 

 to the degree of concentration of the ganglia, 

 in the different classes of this sub-king- 

 dom, that it is of little consequence what 

 example we select. It will be convenient 

 to take for illustration that of the Larva of 

 the Sphinx ligustri, or Privet Hawk-Moth, 

 which has been minutely described by Mr. 

 Newport. Here we observe a chain of 

 ganglia running from one extremity of the 

 body to the other, along the ventral sur- 

 face, and in the median line. These gan- 

 glia are connected by trunks, which, on 

 close examination, are seen to consist of 

 two cords closely united. The cephalic 

 ganglion is bilobed ; evidently consisting 

 of two masses, which are united on the 

 median line. These receive the nerves of the 

 eyes and antennae ; but they are still of small 

 size, in accordance with the low develop- 

 ment of the sensory organs. The ganglia 

 of the longitudinal cord are nearly equal 

 from one extremity of the body to the 

 other. Each sends off nerves to its re- 

 spective segments ; and the branches pro- 

 ceeding from the different ganglia have 

 little communication with each other. The 

 highest of them, situated just beneath the 

 oesophagus, is connected with the cephalic 

 masses by two cords ; between which that 

 canal passes, encircled, as it were, in a ring. 



326. The most detailed account of the 

 conformation of the Nervous Centres in 

 the Articulata, is that recently given by 

 Mr. Newport, in regard to the lulus, and 

 other animals of the class MYRIAPODA.* 

 Their general arrangement corresponds 

 with that which has been just described 

 in the larva; of the Sphinx ligustri ; but 

 the number of ganglia is much greater. In 

 each lateral half of the cord, two distinct 

 tracts or layers of librcs can be detected : 

 of these, one known as the fibrous tract 

 is continuous with the cephalic ganglia, 



* Philosophical Transactions, 1843. 



