=Structure of the mushroom bodies.=—By staining the brain of the honey bee with bichromate of silver, Kenyon has worked out the structure of the mushroom bodies, with their cells. The cup-shaped bodies or calyces are composed of fibrillar substance (_punktsubstanz_). Each of these cups, he says, is “filled to overflowing with cells having large nuclei and very little cytoplasm.” From the under surface of each of these cups there descends into the general fibrillar substance of the brain “a column of fibrillar substance, which unites with its fellow of the same side to send a large branch obliquely downward to the median line of the brain, and an equally large or larger branch straight forwards to the anterior cerebral surface.” The cells of the mushroom bodies, observes Kenyon, “stand out in sharp contrast to all other nerve cells known, though they recall to some extent the cells of Purkinje in the higher mammals. Each of the cells contained within the fibrillar cup sends a nerve-process into the latter, where it breaks up into a profusely arborescent system of branchlets, which often appear with fine, short, lateral processes, such as are characteristic of the dendrites of some mammalian nerve-cells.” Just before entering the fibrillar substance, a fine branch is given off that travels along the inner surface of the cup along with others of the same nature, forming a small bundle to the stalk of the mushroom body, down which it continues until it reaches the origin of the anterior and the inner roots above mentioned. “Here it branches, one branch continuing straight on to the end of the anterior root, while the other passes to the end of the inner root. Throughout its whole course the fibre and its two branches are very fine. Nearly the whole stalk and nearly the whole of each root is made up of these straight, parallel fibres coming from the cells within the cup of the mushroom bodies. What other fibres there are enter these bodies from the side, and branch between the straight fibres very much as the dendrites of the cells of Purkinje branch among the parallel fine fibres from the cells of the granular layer in the mammalian cerebellum. These fibres are of the nature of association fibres.” Viallanes showed that from the olfactory or antennal lobes, as well as from the optic ganglia, there are tracts of fibres which finally enter the cups of the mushroom bodies, and Kenyon has confirmed this observation. Kenyon has also, by the Golgi method, detected another tract, before unknown, “passing down the hinder side of the brain, from the cups to the region above the œsophagus, where it bends forward and comes in contact with fibres from the ventral cord, which exists, although Binet was unable to discover any growth of fibres connecting the cord with the brain.