My friend Mr. W. B. Hardy has especially investigated the nervous system of Artemia. In the course of his work he cut serial sections through the whole animal, and, as mentioned in my paper in the _Journal of Anatomy and Physiology_, he discovered that the retinal ganglion of each lateral eye is so closely attached to the end of the corresponding diverticulum of the gut that the lining cells of the ventral part of the diverticulum form a lining to the retinal ganglion (Fig. 45). In this animal there are only two gut-diverticula, which are situated most anteriorly. I have plotted out this series of sections by means of a camera lucida, with the result that the retina appears as a bulging attached ventro-laterally to the extremity of each gut-diverticulum, as is shown in Fig. 46. It is instructive to compare with this figure Scott's picture of the developing eye in Ammocoetes, where he figures the retina as {112}a bulging attached ventrally to the extremity of the narrow tube of the optic diverticulum. In Fig. 47, A, I reproduce this figure of Scott, and by the side of it, Fig. 47, B, I have represented the origin of the vertebrate eye as I believe it to have occurred. We see, then, this very striking fact, that in the most primitive of the Crustacea, not only are there two anterior diverticula of the gut, but also the retinal ganglion of the lateral eye is in specially close connection with the end of the diverticulum on each side. In fact, we find in the nearest living representative of the trilobites a retina and retinal ganglion and optic nerve, closely resembling that of the vertebrate, in close connection with an epithelial tube which has nothing to do with the organ of sight, but is one of a pair of anterior gut-diverticula. It is impossible to obtain more decisive evidence that the trilobites possessed a pair of gut-diverticula surrounded to a greater or less extent by the retina and optic nerve of each lateral eye.