120 Mr. P. A. Buxton on the 



pass to the opposite side of the brain, to the antennary lobe 

 or head of the mushroom body, or even into the optic 

 lobe. Inside the brain are found small cells, lying singly 

 or in groups (Plate X). Kiihnle refers to them as 

 neuroglia cells (ng.) and doubtless he is correct in so doing. 

 They are found particularly in the space surrounding the 

 central body and in the interval between the two capsules 

 of that organ ; there are also a few on the surface of the 

 stem of the mushroom body and in other places (PI. X). 

 The nucleus of a neuroglia cell is pyriform or elongate and 

 stains deeply, and its outline is generally irregular. The 

 nucleus is smaller than that of a " normal " ganglion cell. 



The axons from the ganglion cells enter the axonic part 

 of the brain vertically ; and they are generally united into 

 small bundles at their point of entrance. It is to this that 

 Kiihnle gives the name Einsirdmmung. 



Spherical black granules occur among the cells in material 

 fixed in osmic acid, or any mixture containing osmic 

 acid. These granules are not found in material fixed in 

 any other fluid, and I regard them as unsaturated fat. 

 They are found among the ganglion cells and are quite 

 definitely extracellular. 



A note on technique is given at the end of the paper; 

 suffice it to say here the cells may be studied in material 

 fixed in the picro-chlor-acetic fluid, but that some specimens 

 may with advantage be fixed in Bouin's or Gilson's fluids, 

 especially for the study of the different types of cell. 



Tracheation. — In the brains of most insects fine 

 tracheal trunks can be detected ramifying in the fibrillar 

 part of the organ. This is not the case in Micropteryx, 

 perhaps because of the extremely small size of the whole 

 insect : so far as I can discover there are no tracheae at all, 

 either in the ganglion cell layer or the axonic fibrillar part 

 of the brain. There is a considerable collection of tracheal 

 trunks {Ir.) in the neurilemma which lies over the mid-dorsal 

 part of the brain (Plate X), and it is at least possible that 

 it is the function of these trunks, which are large and 

 numerous, to oxygenate the brain by diffusion through the 

 fluid which lies beneath the neurilemma. 



II. The Protocerebeal Lobes. 



The protocerebrum of insects is generally described as 

 consisting of the protocerebral lobes and the various 

 structures such as the mushroom body, the central body, 



