112 THE INTEGUMENTAL SKELETON OE THE IMAGO. 



view cannot be maintained if the alimentary tract represents 

 the central canal of the nervous system. The great corpora 

 fungiformia more probably represent the cerebellum. The 

 post-oral metameral ganglia, from which all the true nerves 

 arise, are infra-oesophageal, and probably, with the thoracic 

 ganglia, correspond to the medulla oblongata. The loss of co- 

 ordination due to the destruction of these ganglia is no argu- 

 ment, as it is impossible to destroy them without destroying the 

 peduncles of the supra-oesophageal ganglia. 



The manner in which the fibres of each crus diverge and 

 form three bundles has not, so far as I know, been observed 

 by previous v/riters ; these three bundles correspond to the 

 three sections of the brain : the anterior bundle goes to the 

 fore-brain, the middle bundle to the mid-brain, and the great 

 posterior bundle forms the stem of the internal and external 

 calix of the corpus fungiforme. 



This divergent arrangement of the nervous cords which form 

 the crura is clearly indicative of an arrangement of the centres 

 in front of the mouth, not in a linear series, but as a divergent 

 series all equally related to the segmental neuromeres. 



In the brain of the more generalised Insecta — as, for example, 

 that of the Cockroach {Periplaneta) — the trabeculae {Balken) 

 appear to me to represent the thalamencephalon, the cauliculi 

 {Vordcrhorn) the corona radiata, and the peduncles {Hintcrnst) 

 the superior peduncles of the cerebellum. 



The oesophagus lies below the ventricle of the cerebroid 



Description of Plate V. 



A series of diagrams illustrating the theoretical structure of the skeleton in insects. 



Fig. I. — Side view. 



Fig. 2. — Median section. 



Fig. 3. — Ventral view, with the integument removed on the right side to show the 

 nerve centres : a, antenna : a cc, anterior cephalocele ; e, compound eye ; efc, 

 epicephalon ; /■', /-, /', thoracic legs ; ?nd, mandible ; mx^, maxilla ; nix-, second 

 maxilla ; mes /, mesolabrum ; //, prelabrum ; p cc, posterior cephalocele ; fa c, 

 paracephalon ; .r*, s^, s^, 4th, 5th, and 6th somites ; st, stomodaeum ; I. to VI., 

 neuromeres of the ventral chain ; i, antennal ganglion ; 2, upper part of the crus 

 of the cerebron ; j, corpus fungifoime ; 4, median commissure surrounded by 

 the central ventricle ; J, cerebroid ganglia ; 6, optic ganglia ; 7, commissure of 

 the optic ganglia. 



