Procephalic Lobes of Epciru Ciiicrea. 445 



cup-shaped depression, and becomes the retina of the eye (p. m. e. 

 and I. e.). 



The larger and more superficial regions of the procephalon consist 

 of the optic ganglia which overlie the anterior and lateral optic 

 vesicles, as well as the ganglia of the cerebral lobes. 



V. FuHiMATION OF THE AdULT ]>KAIN. 



The procephalic portion of the brain of Epcira is a structure of 

 considerable complexity, consisting of two lateral, pear-shaped lobes 

 which are separated by a deep longitudinal furrow. (Text-fig. 2; 

 0. I.). As we have seen, however, in following the development of the 

 brain, each of these lobes consists of optic ganglia and optic vesicles, 

 which constitute the greater part of their superficial area (Fig. 27; 

 opt. g.). The lobes formed by the cerebral ganglia lie underneath the 

 optic ganglia (Fig. 27; c. r/L). The short, thick, column-like con- 

 nectives on either side of the oesophagus, which unite the procephalic 

 and postcephalic portions of the brain, represent the contribution of 

 the cheliceral segment to the cerebrum of the spider. 



Below the oesophagus is a mass of ganglia consisting of neuromeres, 

 some of which belonged originally to the abdominal segments (Fig. 

 34; s. 0. g. 1-12). Their position in the head region is one of the 

 results of the reversion of the embryo, which caused them to be 

 pushed forward into that place. These ganglia are imperfectly fused, 

 even in the adult, a fact which facilitates their determination. The 

 first four of these sub-oesophageal ganglia arose in connection with 

 the thoracic segments, the rest having been crowded forward into the 

 thoracic region from the places where they originated in connection 

 with the segments of the abdomen. 



These observations bring the brain of Epeira into close accord with 

 the researches of St. Remy and Patten. St. Remy speaks of the 

 procephalic portion of the brain as consisting of a rostro-mandibular 

 part (cheliceral ganglia), and a much larger optic ganglion which 

 consists of the principal i)ortion of the supra-oesophageal mass. Tn 

 the optic ganglion he found three distinct divisions, the first of these 

 he calls the optic lobe. The second he calls the cerehral Johe. Behind 

 these lies the unpaired organ slratife which, together with the optic 

 ganglia, comprises what I have called the optic lobe. 



