1880. ] Zoölogy. 447 
at intervals. 4. Rounded masses, consisting wholly of nuclei, 
enclosed in a network of fibres, which stain dark brown with 
osmic acid; these bodies form the larger part of the substance 
of the brain, while staining dark brown with osmic acid; in un- 
stained alcoholic sections these masses are dark or grayish, the 
substance or fibres enclosing them, being whitish, by transmitted 
light. The brain is enveloped by a thick perineurium, formed 
of a fibrous tissue, and some (probably) elastic tissue, which oc- 
casionally penetrates into the brain-substance between the white 
rounded fungoid masses, forming the mesh-work surrounding 
them. The general topography of the brain of Limulus is on a 
simple plan compared with that of Decapodous Crustacea and in- 
sects. The brain is mostly composed of large irregular rounded 
masses or balls of nuclei, with a thick fungoid or ruffle-like 
periphery, formed by a layer of secondary smaller rounded granular 
masses. The center of the primary masses is stained paler brown 
by osmic acid. These masses are often seen in section, rounded, 
but more often are irregular, not closed spheroids; these fungoid 
which spring from them, becomes larger from the upper third to 
the top of the brain where the optic fibres originate. Opposite 
the beginning of the optic nerves, these large nerve fibres are seen 
directed towards the origin of the nerves as if they were the roots, 
as they undoubtedly are. In the section passing through the 
ocellar nerve and the tegumentary nerves on each side, the fun- 
goid masses are situated in the front of the brain; but they dis- 
appear from the front higher up at the origin of the optic nerves, 
and occupy a much more restricted area on the sides of the brain. 
Thus the tract of nerve fibres on either side of the brain is irreg- 
ularly wedge-shaped, the apex situated near the centre of each 
hemisphere, and the base spreading out on the top, thus crowd- 
ing to the outer walls the nucleogenous bodies. 
_ It would thus appear as if the lower half of the brain were in an 
indifferent state,’ and that the dynamic part were confined to the 
upper third, the region giving origin to the nerves of sensation. 
1 This area, made up of granules and nuclei, seems really to be connective tissue, and : 
to represent the connective tissue in which the ganglia of the embryo of the young 
larva are embedded. There seems no reason why the brain should not be partly 
formed from connective tissue as much as the remaining ganglia, as we have seen 
them to be in different sections of different ganglia, all or nearly all except the supra- 
cesophageal one. 
