Protocerebrum of Micropteryx. 137 



possibly also to the tritocerebrum and the ventral parts of 

 the central nervous system (PI. VII, figs. 2-4). 



(6) A tract of fibres which is the Riechstrang, or Riech- 

 bahn, of the German authors. The cells from which the 

 tract arises appear to be ganglion cells of the " normal " 

 type, and are situated dorsal to the protocerebral lobes 

 and slightly behind the head of the mushroom body : the 

 fibres pass downwards and forwards and slightly inwards, 

 through that part of the protocerebral lobes which surrounds 

 the space containing the central body, etc. ; from here the 

 fibres are directed downwards and outwards to the anten- 

 nary lobe. Through most of their course the fibres lie 

 in a free space. Owing to its diftuse structure, which ren- 

 ders it difficult to distinguish it when it is cut transversely, 

 the lower part of this tract can only be distinguished in 

 longitudinal section (text fig. 3, D and E, p. 129). 



(c) A broad anterior commissure (PI. VII, fig. 6). 



{d) A deep commissure. 



(e) A double ventral commissure (the vordere und hintere 

 Brucken der N ehenla'p'pen unter sicli of Kiihnle; PL 

 VIII, fig. 9). These three are the most definite tracts 

 which unite the two sides of the protocerebrum, though it 

 should be remembered that the lobes are united over the 

 greater part of their internal aspects, and that a large 

 number of smaller tracts pass from one side to the other. 

 These three tracts form the boundary of the " loge " in 

 front, behind and below : the anterior and ventral ones lie 

 upon the surface of the fibrillar part of the brain, the deep 

 commissure passes between the two protocerebral lobes 

 behind the " logs " : the ventral commissure (e) arises on 

 each side from the anterior part of the ventrolateral lobe. 



(/) A small but distinct band of fibres which runs trans- 

 versely across the upper surface of the " logs." This tract 

 is the Faserhof oi Kiihnle, and possibly also the commessura 

 jprotocerebmie anteriofe of Berlese (PI. VIII, fig. 8). 



(g) A posterior commissure uniting the two protocerebral 

 lobes at their most posterior part, where they overlap the 

 tritocerebrum (PI. IX, fig. IG). 



{h and i) Tracts uniting respectively the anterior part 

 of the middle lobe to the anterior part of the ventro- 

 lateral lobe, and the posterior part of the middle lobe to the 

 posterior part of the ventrolateral lobe of the same side. 



(j) A tract running from the posterior part of the middle 

 lobe to the deuterocerebrum. 



