PACKARD.] MORPHOLOGY OF PHYLLOPODA. 381 
fragmentary and superficial. The eyes are closely approximate, ap- 
pearing as a single eye. Unlike that of Hstheria the number of lenses 
is small. Plate HU, fig. 6, represents the eye of Limnetis gouldii, a circle 
of erystalline lenses surrounding the central pigment mass or retina. 
The lenses are contiguous, the pigment not extending between them as 
in Artemia, Plate XXIII, fig. 6. Plate IJ, fig. 5, represents the two 
optic nerves and optic ganglia, the cornea with the crystalline lenses 
and pigment layer having been torn off with the needle. The optic 
nerves are very thick, and instead of, as usual, being composed solely 
of nerve fibers, appear to be largely made up of nerve cells; fig. 5 @ 
represents an enlarged view from near the middle of the optic nerve, which 
is made up almost wholly of strings of nerve cells. Toward the distal 
ends of each optic nerve converge delicate fibers which connect the cells 
of the optic ganglion with the optic nerves. An enlarged view of the 
optie ganglion is seen in Plate X XIX, fig. 9. The ganglion cells are not 
very numerous nor crowded; they are nucleated and nucleolated, and a 
nerve-fiber broad, triangular next to the cell, rapidly diminishes in size 
towards the middle of the fiber. It is interesting to notice the inter- 
communication in the median line of the head between the two eyes; a 
small number of cells on the opposing edges of each eye are seen to send 
’ transverse nerve-fibers (fig. 9, tr. m.) across to the opposite optic gang- 
lion; though externally the system of crystalline lenses do not quite 
touch each other. We have not examined the crystalline lenses of 
Timnetis. 
The eye of Estheria is nearly on the same general plan as in Limnetis. 
Lenz has discovered that the lenses are composed of five segments, in- 
stead of two, the usual number in Crustacea, particularly Apus and 
Branchipus. 
The inner structure of the eye of Artemia was studied on the living 
specimens, Plate XXIII, figs. land 6. Fig. 1 shows the general relation 
of the sessile square simple eye and of the stalked compound eyes to the 
head and also to the brain. Fig. 6 represents the relations of the eye 
and its optic lobe to the eye-stalk of the living animal. The optic nerve 
is in the center; the large rectus muscle of the eye is situated on the 
hinder or outer side of the stalk, arising near the brain and being in- 
serted on the cornea at the base of the eye near the first crystalline lens; 
the exact mode of insertion was not observed. The blood circulates 
freely, flowing from the head along the anterior side of the outstretched 
eye, the corpuscles, of different sizes and not very numerous, passing be- 
tween the optic nervules (op. n.) and returning, as the arrows indicate, 
along each side of the rectus muscle back to the head. 
The general structure of the eye of Artemia gracilis is much as repre- 
sented by Leydig in Branchipus stagnalis ; the ganglion opticum, how- 
ever, is in our specimen of Artemia composed of but a single mass, not 
of two distinct masses connected by coarse nerve-fibers., From the 
ganglion opticum about a dozen optic nervules penetrate the retina, which 
is larger in proportion to the eye than represented in Leydig’s figure; 
the superficial circle of crystalline lenses or cones showing very plainly. 
The question as to whether the eyes of Crustacea, particularly the 
stalked eyes, are homologous with the other appendages, and thus rep- 
resent distinct segments of the head, and which is still held by some 
naturalists, may, it seems to us, be set at rest by examining the eyes of 
Phyllopod Crustacea. In the Limnadiada and Apodide, where the eyes 
are sessile, it is easy to see, particularly in Limnetis and Limnadia, that 
the eyes are modified epidermal cells covering the ends of the optic 
nerves. They are situated on the front or upper walls or tergum of the 
