Protocerehrum of Micropteryx. 125 



culties are rather apparent than real, and that Micropteryx 

 is really one of those organisms from the study of which 

 we may draw valuable inference as to the comparatiye 

 anatomy of the insect brain. It is always a most difficult 

 thing to form a picture of the mushroom body of an insect 

 when that organ is described by another worker. This is 

 due, in part at least, to the complexity of the organs which 

 lie in all three planes of space. I shall endeavour to make 

 my meaning clear by giving several sketches of a mental 

 reconstruction of the organ in question. Its structure in 

 Micropteryx is comparatively simple, and I have not found 

 it necessary to make a wax-plate model. I have, of course, 

 most carefully examined sections in all three planes of 

 space (text figs. 2, 3, pp. 128-9). 



The head of the mushroom body of Micropteryx is a single 

 globular mass of axonic tissue, and belongs to the Hocker 

 type of Kiihnle. It appears that a similar structure was 

 described by Flogel in certain moths ; but it is never easy 

 to understand his descriptions, for he was much hampered 

 by the defective methods of his time. 



The head of the mushroom body {hd.) projects conspicu- 

 ously into the ganglion cells above and behind. It is not 

 so large, however, as to make a prominence in the upper 

 surface of that layer. 



From the cells of the mushroom body (p. 119) the fibres 

 pass into the head of the mushroom body. We must notice 

 that there are no points at which a number of fibres enter 

 together; the entry is general and spread over the w^hole 

 surface of the head. Kenyon's application of the Golgi 

 method to the brain of the bee makes it clear that after 

 entering the substance of the head the fibres give off a 

 collateral branch which in turn divides to form twigs. 

 These twigs interlace with similar twigs from the collaterals 

 of other cells to form a glomerular body {FaserbdUchen). 

 There must be several score of these bodies in the head of 

 the mushroom body of Microjiteryx. They are very small 

 and by no means easily distinguished. After giving oft' 

 its collateral the fibre proceeds downward as a component 

 part of the stem. The fibres do not form a definite tract 

 within the head, but pass through in a diffuse manner. It 

 is only when they reach the underside that they unite to 

 form the stem. 



From the inner and inferior aspect of the head of the 

 mushroom body a band of fibres sweeps downwards and 



