Protocerebrum of Micropteryx. 123 



Special nauTes liave been assianed to various parts 

 of the protocerebrum (refer to PI. VII-IX). Thus dorsally 

 there is the dorsal lobe (Hcmptlappe), below this the ventro- 

 lateral lobe or Nebenlappe, and niidventrally the middle 

 lobe {Mittelstilck). These parts may all be distinguished 

 in Micropteryx, and perhaps the mere shape of the lobes 

 merits description. The dorsal lobe {d.l.) is the widest 

 part of the whole brain. In front its superior surface is 

 flat ; further back there is a specialised rounded projection 

 in the middle line, to which I give the name Tumulus {tu.). 

 This lies between the heads of the two mushroom bodies, 

 and consists of a very tight homogeneous web of axonic 

 substance more densely compacted than any other part of 

 the brain. The portions of the dorsal lobe which lie around 

 and beneath it are of an extremely loose consistency 

 (see PI. X). 



A large lateral lobe {I. I.) is present on each side.* Its 

 relations are shown in figs. 10, 12, 13. 



The ventrolateral lobes {Nebenlappe) consist of two very 

 definite parts placed one in front of the other. The anterior 

 part of the ventrolateral lobe {v.l.l.a.) appears as a swelling 

 below the anterior extremity of the stem of the nmshroom 

 body ; in the region beneath the inner root of the nmshroom 

 body the lobe is insignificant ; and behind this its posterior 

 part (v.l.l.p.) appears as a large round lobe above the exit 

 of the motor antennary nerve from the deuterocerebrum. 



The middle lobe {mi. /.) of the protocerebrum lies between 

 the two ventrolateral lobes. In most insects it consists 

 of a single body, shaped like an hour-glass, and lying 

 transversely between the inner roots. In Micropteryx 

 we can distinguish an anterior and a posterior part of the 

 lobe. The anterior portion {mi. I. a.) is of the shape of an 

 hour-glass, and hes, as it should, between the ends of 

 the inner roots ; it is connected with the anterior part 

 of the ventrolateral lobe on the same side by a tract 

 of nerve fibres (tract h). Behind it there is a transverse 

 bar of axonic tissue, placed below the ocellary glomeruli 

 and above the various bands which connect the two anten- 

 nary lobes or deuterocerebra ; this is the posterior part 

 {mi. I. p.) of the middle lobe; to the antennary lobe and 

 also to the protocerebrum above it this middle lobe is 

 united by well-marked tracts of nerve fibres (tracts ji and k). 



* This is not le lobe lateral du protocerebron moyen of Viallanes, 

 which is the ventrolateral lobe. 



