This Atlas is addressed not only to specialists of Arthropod neuroanatomy and neurophysiology, but to anyone interested in the general structure of brain. Originally, it was planned to encompass several species of insects in order to show similarities and differences between them: but in practice such an under­ taking would have demanded a volume three times the present size, an exercise both prohibitive in cost and in material. And had it been accomplished it would have merely concussed all but the most persevering readers. Since my intention is not to stun but to enlighten, I have consequently restricted the main contents of this book to one species, Musca domestica, the common house fly. The Atlas attempts to illustrate the main neuropil regions of the fused cephalic ganglia as well as to define the main tracts and many single neurons which contribute to their structure. Since the accounts of FU)GEL in 1876, VIALLANES in 1884 and KENYON in 1896 and 1897, all three workers veritable Ptolemys of insect neuroanatomy, only the description of POWER comes near to modernizing our knowledge of the general dispositions of the main neuropil masses. And as far as I am aware, apart from the now classic work of reference by BULLOCK and HORRIDGE: Structure and Function in the Nervous System of Invertebrates, there is no contemporary work which lists, in a concise way, the various terminologies used for brain regions.