205 



inal axes of the two suboesophageal ganglia do not form a 

 continuous line, but are so directed as to form a very obtuse 

 angle opening downward, as may be seen in the figure. This 

 deflection in the nervous axis helps to increase the differences 

 already noticed in the dorsal and ventral outlines connecting 

 the ganglia. This ganglion also presents both anterior and pos- 

 terior indentations, as well as slight longitudinal depressions in 

 its dorsal and ventral surfaces, indicative of its origin from 

 lateral halves. ,It is under the anterior end of this ganglion 

 that the two ducts of the salivary glands unite and eventually 

 open into the beginning of the oesophagus. (See figure.) 



The circumoesophageal commissures are comparatively long 

 and slender. Their direction from the lower anterior aspect of 

 the first suboesophageal ganglion is — unlike that of most 

 arthropods — obliquely doumward and forward. In their course 

 they pass beneath a chitinous frame-work,^ and ultimately di- 

 verge to reach the infero-postei-ior surface of the two halves of 

 the brain SJinfflion. 



The ganglionic pair which constitutes the superoesophageal or 

 brain-mass presents considerable variations, from a rather in- 

 timate union of the two halves^ to such a condition as is re- 

 presented in the accompanying figure, where the lateral halves 

 are joined by a brain-commissure of considerable length and 

 of not much greater thickness than that of the circumoesoph- 

 ageal commissures. Although my observations were not suf- 

 ficiently extensive to exch;de the possibility of an erroneous 

 inference, I still think that these two forms of the brain-mass 

 belong respectively to the wingless and winged individuals. So 

 much, at least, is certain, that the figure here presented was 

 made from one of the winged insects, and that all my drawings 

 of the wingless forms show a much closer approximation of the 

 two halves. 



It can be in no way a source of surprise that the brain-mass, 

 in the wingless form, is, moreover, considei'ably smaller than 

 in the winged form, when one reflects on the greater develop- 



1 The anterior portion, or cross-piece, of this frame work is what I have called arcus 

 superior, and the lateral portions costae superiores, in the paper above referred to. 



2 Much as in Aspidiotus nerii. Vide op. cit., Taf. VJ, fig. 31, gjy. 



