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Volumetric and histological changes of the central nervous system were studied during post embryonic development of a spider, Argiope aurantia.The neural mass of Argiope grows allometrically with respect to volume of the cephalothorax and body weight. In the first instar 46% of the cephalothoracic volume constitutes the neural mass and this is reduced to 4 % in the female (9th stage) and 12% in the male (7th stage) spider.Growth curves for the cephalic ganglion, measured at all stages, represent a straight line. The neural mass of females is two and a half times larger than that of the males. The ganglion increased 24 fold in female and 10 fold in male spiders. Addition of neural mass occurs in all stages. The brain volume is greater than that of the subesophageal ganglion in the first two instars. In subsequent stadia, the subesophageal ganglion grows faster, and in females it is finally three times and in males two times larger than the brain.Growth of cortex and neuropile depict exponential curves. Comparison of Although the spiders have been used for cock ('02), Haller ('12), Hilton ('lZ), Buxseveral kinds of experimental studies, the ton ('17), Gerhardt and Kaestner ('37), post embryonic development of their central Millot ('49), Legendre ('53), Firstman ('54) nervous system has received little attenand Babu ('65, '69). Its histology and tion. However the nervous system of the adult spider has been the subject of several investigations. lts external morphology was described by Blanchard ('59), PO-This paper is dedicated to the memory of Prof. K. Pampapathi Rao on the fust anniversary of his death. Present address: Department of Zoology, Sri Venkateswara University, Tirupati, Andhra Pradesh, India. J. MORPH., 146: 3 2 5 3 4 2 . 325 I Q! a 4ld J u 3 z 3 -2 -TYPE-B 9 \ \ 0-0-0-\