32 A. S. PACKAED, JR., ON THE ANATOMY 



At the uppermost region of the brain the sides are occupied by the nucleogenous bodies 

 (nb), extending nearly to the back of the brain, but not reaching near the front. 

 Within, but next to tliese nucleogenous bodies, are large sub-spherical masses of nu- 

 cleated cells (fig. 1, cm), from which the optic nerves apparently arise. (Only the outer 

 edge of the left mass has been cut through.) These cells are abundant and represented 

 by fig. 2. They are hyaline, contain few granules, as do the nuclei. They are a 

 little smaller than those of the lobster, which we have drawn to the same scale with 

 the camera lucida, bvit it will be seen that they are identical morphologically. En- 

 closing in part the left mass of cells is a Y-shaped mass of fibres and nuclei (?/) which 

 reminds one of the trabeculae of the cockroach's brain. This apparently is not of much 

 importance, and is an oft-shoot from the central mass of nerve-fibres, as in five sections 

 below, it merges with the other fibres. Just behind the middle of the brain, on each side 

 of the median line, is a group of large ganglion-cells adjacent to the rounded cellular 

 masses. Behind each group of large ganglion-cells originate the fibres of the com- 

 missures connecting the brain with the oesophageal ring ; on the outside of the com- 

 missural nerve-fibres is a group of large ganglion cells longitudinally disposed. As we 

 descend from the top to the base or under side of the brain, the commissure is cut 

 through and disappears, the brain extending considerably below the oesophageal ring. 



In the next section the large ganglion-cells are seen to be scattered through the middle 

 of the posterior fibrous portion of the brain. 



In the tenth section two large ruffle or fungus-like nucleogenous bodies appear, one on 

 each side of the median line, with several smaller ones ; and at the back part of the brain 

 a bridge or transverse bundle of fibres now appears, connecting the mass of nerve-fibres 

 on each side of the brain. This bridge becomes thicker as seen in the fourteenth 

 section (plate 7, fig. 2). 



This latter section passes through the lower edge of the right optic nerve (op n). 

 The fibrous region is now invaded more than above by the nucleogenous bodies {iib), the 

 former being mostly restricted to the posterior half of the brain, the brain itself being 

 longer, and the oesophageal opening not extending so far into the middle of the brain. Its 

 bilateral symmetry is seen to be tolerably marked. The Y-shaped fibrous mass is broad 

 and obscurely marked; while the nucleogenous bodies occupy nearly two-thirds of the 

 area of the section, the area having extended from the sides around to the front, nearly 

 meeting on the median line of the brain. There are two central areas containing large 

 ganglionic cells, and two other similar areas farther back and nearer the sides of the 

 brain. 



Plate 7, fig. 1«, represents the size of the large ganglion-cells of Limulus, compared with 

 fig. lb of a similar cell from the lobster's brain ; the two being identical in size and in den- 

 sity of the protoplasmic granules. 



Plate 7, fig. 3, represents a section through the front part of the right side of the 

 brain ; it shows the origin of the optic nerve from the small sized ganglion-cells in the 

 central region of the brain. That the nerve-fibres within the brain are sometimes nucle- 

 ated is shown by the adjoining figures (3a, Sb), where the nerves are cut transversely. 



Plate 7, fig. 4 represents a section through the ocellar nerve, just grazing the right teg- 

 umental nerve. The fibrous portions are still more restricted, and they extend to the 



