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in shape from the full well developed sub-spherical shape of those of 

 Arachnids. They are narrow and thin, sending off lateral irregular 

 lobules, and connected posteriorly by a thick commissure. This com- 

 missure, as numerous sections show, consists of fibrillae originating 

 from the , as seen in section , crescent-shaped , central dense mass of 

 chromatic cells near the posterior margin of the brain, and which 

 overlies the median line of the great commissures leading to the oeso- 

 phageal ring. 



The central mass of the cerebral lobes does not pass much below 

 the middle of the brain: but the posterior lobules on each side serve as 

 the origin of the great commissures connecting the brain with the 

 oesophageal ring, Avhich is formed by the coalescence of the neuromeres 

 of the post-oral cephalo-thoracic appendage-bearing segments. 



We thus have been able to distinguish three pairs of lobes in the 

 brain of Limulus viz.; those of the lateral, those of the median eyes, 

 and the cerebral lobes. 



Professor Patten describes and figures three eye-segments in the 

 embryo ; a first and second median-eye segment and the lateral eye- 

 segment, and gives an interesting figure based on dissections and 

 sections, of the »fore and mid-brain« of the freshly hatched Limulus 

 The three pairs of neuromeres, he claims, succeed one another in re- 

 gular order. 



But afterwards this order is greatly changed; for the median eye- 

 lobes are carried during subsequent growth down in under the lateral- 

 eye lobes, the latter being far removed from each other and assuming 

 a position anteriorly and at the top of the brain. 



It is noteworthy that the rounded under side or base of the brain, 

 which sinks below the level of the commissures to the oesophageal 

 ring, is almost Avholly occupied with densely packed nucleogenous 

 bodies , or chromatic cell-masses , which are enormously developed 

 compared with the similar bodies in the Arachnid brain. On the other 

 hand the large normal ganglion cells are mostly grouped in one plane, 

 that of the origin of the commissures to the oesophageal ring, to whose 

 fibrillae the give origin. In the brain of the scorpion and spiders these 

 cells as figured by Saint Remy, form a large part, more than half, 

 of the cortical substance enclosing the lobes. 



It will be seen from the foregoing description that the brain of 

 the adult Limulus differs from that of Arachnids not only in not sen- 

 ding a pair of nerves to the first pair of feet, but in the structure of 

 the brain itself, though on the whole it resembles that of Arachnids 

 more closely than that of Crustacea. 



The brain, or supraoesophageal ganglion, of Insects and Crustacea 



