3T 



(Plate IV., fig. 36). At its commeucement it is in the 

 form of a closed canal (Plate II., fig. 26), which appears 

 to have been developed by the union with one another 

 of a pair of parallel ridges of the cuticle ; traced 

 further backwards, in the prothorax, the canal is 

 incomplete, the ridges not having fused with one 

 another ; in the metathorax each ridge has been folded on 

 itself, and the two together form a j)air of tubes with a 

 groove or channel between them (figs. 24 and 26t'), and in 

 this condition it continues the remainder of its course on 

 to the ventral tube. 



The secretions of the tubular and acinose glands fiow 

 down the groove to reach the surface of the ventral tube, 

 which they serve to moisten. The fact that the ventral 

 tube receives the secretion of cephalic glands was first 

 ascertained by Fernald, and, although doubted by other 

 investigators, it has been recently confirmed by both 

 Willem and Hoffmann. Fernald, however, appears to 

 have regarded what are here described as salivary glands 

 as being the glands which furnish the secretion, and what 

 he has regarded as their ducts opening into the ventral 

 groove, appear to be really the ducts of the tubular 

 glands. 



8. The jSTervous System. 



The nervous system consists of a chain of five ganglia 

 united together by means of a double series of nerve 

 cords or connectives (Plate IV., fig. 48). The first of these 

 is the supra-oesophageal ganglion or brain ; it is situated 

 in the head immediately above the oesophagus (fig. 35). 

 The remainder of the system forms the ventral nerve cord 

 and lies beneath the digestive canal. It comprises a large 

 sub- or infra-cjesophageal ganglion, which is t()lh)wed by 

 three ganglia, lodged respectively in the prothorax, the 



