AND EMBRYOLOGY OF LIMULUS. 33 



insertion of the nerves; the fibres are arranged into transverse as well as longitudinal 

 bundles, of which the more important ones are figured, but of their origin and termination 

 nothing definite has been ascertained. 



Plate 7, fig. 5 represents a section through the middle of the ocellar and two tegumental 

 nerves, and though it is ob\'ious that the razor cut tolerably even, as the nerves are quite 

 evenly severed, yet it will be seen how unsymmetrical the brain at this point is, after allow- 

 ing for unequal contractions due to reagents. The median line between the two sides is 

 very obscure and irregular ; the mass of large ganglion-cells is quite large, and disposed in 

 an unbroken mass on each side of the median line, should one be drawn through the brain. 

 On the right side the fibres are almost wholly confined to an area near the middle of the 

 right half, while the left side of the brain is mostly occupied with fibres, the nucleogenous 

 bodies not extending to the back of the brain, as on the opposite side. At this part of 

 the brain, in the more symmetrical specimen of the two brains specially studied, the 

 nucleogenous bodies occupy nearly two-thirds of this plane of the brain; while the 

 posterior group of large ganglion-cells is more extensive than above, and there are now 

 but faint traces of the " bridge " of new fibres. 



In a section lower down, near the middle plane of the brain, the nucleogenous bodies 

 extend to the back of the brain, thus enclosing the mass of large ganglion-cells, which 

 lies in front towai'ds the middle of the brain ; the nucleogenous bodies, at least the longer 

 narrower masses, extend in towai'ds the centre of the brain, so that they seem to radiate 

 outwards from near the centre to the periphery. 



In a section through the pair of lower tegumental nerves (fig. 6), in the same brain as 

 represented at fig. 5, and on the same side, the fibrous masses are seen to be greatly 

 reduced in extent, now filling up narrow spaces between the nucleogenous masses which 

 converge towards the interior of the brain. The fibres evidently originate from the 

 smaller and larger ganglion-cells, and pass forward and outward among the rufiSe-like 

 nucleogenous bodies. In the section here figured, the large ganglion-cells extend to 

 the extreme back of the left side of the brain. 



In another section below the nerves (fig. 7), the fibrous portion does not apparently 

 reach the front, nor much beyond" the middle of the brain, which at this point in one brain 

 shows but slight symmetry, no fibres being visible in the right side. 



Just below the section last figured, where no nerves are sent out from the brain, and 

 before the sections diminish in size, the whole area seems to be filled with large rounded 

 nucleogenous fungoid bodies, forming about eight irregular series passing from the back 

 to the front of the brain, and arranged four on a side. A very few small bundles of nerve- 

 fibres are to be seen, but with no determinate direction. This disposition of the histolog- 

 ical elements extends downward to the bottom of the brain. 



A transverse section of the brain from above downwards, cut just before the middle of 

 the brain (fig. 8), shows nearly the same arrangement of parts as in horizontal sections; 

 the upper part is seen to be occupied with the two larger groups of large ganglion-cells 

 (I g c), the nucleogenous bodies taking up most of the remainder of the brain, while a 

 long bundle of nerve fibres (/a) passes from above downwards between the nucleogenous 

 bodies. 



