140 PATTEN. [Vot. II. 
of felted fibrilla, that on the posterior outer side being much 
thicker than the other. If we turn again to the retina of eye 
III., it will be seen that the part on the posterior side of the 
furrow is much broader than that on the opposite, and exceeds 
it in width by about as much as the posterior layer of fibrillae 
in the medulla exceeds that on the anterior side. That this 
extraordinary correspondence between the structure of the eye 
and its medulla is no fanciful one, may be proved by referring 
to any other medulla. In each case, we shall find that she 
structure of the medulla is like that of the retina to which it 
belongs. For instance, in eye V. there are remnants of a me- 
dian row of peculiar cells which undoubtedly represent the 
gigantic cells, such as those in eyes I. and III. In the embryos 
just ready to hatch, the medulla of eye V. is divided in the 
middle by a layer of coarse fibres, the cut ends of which are 
distinctly visible in cross sections, so that the outline of the 
medulla, with its median row of cross fibres, is the mirror-image 
of eye V. with its median row of cells. In the full-grown larva, 
the latter are much smaller and less conspicuous, and we find 
on turning to a section of the medulla that the median row of 
coarse fibres has degenerated in a corresponding degree. 
In eye VI. the upright retinal cells are uniform in structure 
throughout, the median ridge seen in surface views of the 
younger stages having disappeared. But there is a remarkable 
bundle of inverted cells on the ventral side of the retina, and 
this peculiarity is expressed in the medulla of that eye by a 
small bundle of fibres in a corresponding position. Still again 
medulla I. shows by its configuration that it belongs to eye I. 
There is the narrow bent portion belonging to the vertical 
furrow, the broad inner part to the horizgntal retina, and at the 
outermost end of the medulla is a small bundle of fibres belong- 
ing to the appendage. To complete the correspondence there 
are the three rows of fibres in the middle, just as described in 
medulla III., and on either side a layer of medullary substance, 
the thicker layer being on the anterior edge, corresponding to 
the greater width of the retina on that side of the furrow. 
All the optic nerves are composed of coarse fibres arising 
from the medullz. So far as it is possible to determine, each 
fibre is composed of the prolongation of the external and inter- 
nal fibrillee of the cell with which it is united. The latter are 
