Protocerebrum of Micropteryx. 121 



the bridge, the occllaiy glonieruhis, and the optic lobes. 

 The term " protocerebral lobes " is a comprehensive term 

 for the great mass of the protocerebrmn in or upon which 

 the other structures lie. The word " lobes " is perhaps 

 mifortunate, but its use in all papers from an early date to 

 the present day renders it a classical term. In all insects 

 the protocerebral lobes {jjc. I.) form by far the greater part 

 of the brain ; they are bilaterally symmetrical about the 

 middle line, but they are not di\aded from one another by 

 a raphe. Kiihnle describes their fusion across the middle 

 line {Versrhmekung), "above," "below," etc. This is per- 

 fectly accurate, but it would give a clearer impression to 

 say that the two lobes are united over their whole extent 

 at the middle line, except that in the centre a space {la 

 loge, Viallanes) is left in which lie the central body and 

 ocellary glomeruli, and the inner root of the nmshroom 

 body. 



The union of the two sides in Micropteryx is complete, 

 but much less definite posterodorsally. Only a very vague 

 web of fibres covers the central body in this region. It 

 would, for instance, be possible for a micro-organism to 

 swim down from the fluid in which the ganglion cells lie 

 through this web into the space surrounding the central 

 body. The protocerebral lobes together form a rounded 

 mass, with its longest axis in the transverse direction. 

 The mass is flattened above, and prolonged downwards to 

 fuse with the deuterocerebrum and the tritocerebrum. 

 The dividing line between the deutero- and trito-cerebrmn 

 cannot be accurately determined. In the embryo they lie 

 behind one another. In most adult insects, and Micro- 

 pteryx is no exception to the rule, the deuterocerebrum is 

 pushed forwards, and the tritocerebrum fuses directly 

 with the protocerebrum, at any rate by a small part of its 

 posterior surface. From the lateral side of the proto- 

 cerebrum the optic nerve is given oflt. This connects the 

 protocerebrum to the optic lobes (medullary masses of the 

 eye). 



The relations of the protocerebral lobes are as follows 

 (text fig. 1 , p. 122) : mid-dorsally he the rounded heads of the 

 mushroom bodies, and between them the bridge. SHghtly 

 in front of this the ocellary nerve is seen, disposed in a 

 transverse plane with a slight inclination downwards and 

 backwards. Various organs he within the protocerebral lobes 

 in a space full of fluid which has been called la loge by 



