NERVOUS SYSTEM. INVERTEBRATA. 33 



In the lower specimen the nervous system has been ex- 

 posed from the dorsal aspect, the isolated anterior part of 

 another being mounted above. 



D. 25. A Centipede (Scolopendra morsitans) with the integument 

 and muscles removed from the right side so as to give a 

 lateral view of the nervous system. The Hunterian de- 

 scription of this specimen is as follows : " Centipede the 

 brain a small roundish body laid bare : the two great 

 nerves going to the tail with ganglions at the places where 

 they give off nerves, as in the Lobster/' The part above 

 alluded to as the brain is the large suboesophageal ganglion ; 

 the union o the connectives above the oesophagus is not 

 shown. The ventral position of the ganglia and the nerves 

 given off from them are well displayed in this preparation. 



0. C. 1298. Hunterian. 



D. 26. The isolated nervous system of a Centipede (Scolopendra 

 sp.). Preserved in Goadby solution. 



INSECTA. 



Viallanes, Ann. des Sci. Nat., ser. 7, t. xiv. p. 429. 

 Binet, Jour, de FAnat., t. xxx. 1894, p. 449. 

 Brandt, Horae Soc. Entom. Ross., t. xv. 1879, p. 2. 



In the Insecta, apart from the complexity of the cerebral 

 ganglion, one of the most noteworthy features is the variable 

 degree of longitudinal concentration of the ganglia of the 

 ventral chain, either when comparison is made between adults 

 of different species or between the larva and imago of the same 

 species. As a rule the nervous system of the adult is more 

 concentrated than that of the larva. Concentration usually 

 appears first amongst the abdominal ganglia, resulting in the 

 fusion of some at the posterior end of the chain and the in- 

 clusion of some in front in the metathoracic ganglion. The 

 thoracic ganglia also fuse in various ways, though less fre- 

 quently. The pro- and mesothoracic, meso- and metathoracic, 

 or all three, may thus unite. 



Although in some Orders (e. g. Lepidoptera) a certain definite 

 arrangement of the ganglia is fairly constant, in most it is not 



VOL. II. D 



