114 MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 



tered cells and some fibers, the latter layer being quite distinguishable from the cellular layer and 

 reaching nearer the eye.* 



If there were a mass of optic nerves enlarging in bulk towards the retina of the eye, it seems 

 to me we should, out of several hundred sections, horizontal, transverse, and longitudinal, have 

 detected some traces of it, since it is so large in normal Julidse. It would seem that if an 

 optic nerve were present that at least one section would have shown the nerve corresponding to 

 that represented by Graberf in his section of the head of Julus sabidosus. It is still possible 

 that sections of other specimens may reveal a more or less developed optic nerve sending fibers to 

 each facet. 



The eyes are represented by the corneal lenses, the ends of which are buried in the thick, 

 well-developed retinae. Whether any retinal rods and cells, such as those discovered by Gre- 

 nacher,:j: exist in the retina I have not attempted to discover. , The corneal lens appears to be well 

 developed in the case of each facet present. 



PL XXIV, figs. 12 and 13 represent sections still lower down, passing through the facets, but 

 below the optic ganglia. 



In this counectionwe may draw attention to the normal development of the olfactory ganglion 

 and the antennal or olfactory nerve arising from it (PL XXV, figs. 1 to 3). In Fig. 1 the pro- 

 cerebral lobes {pre. I.) and subcesophageal ganglion (sg.) are shown. In Fig. 2 the entire left 

 olfactory ganglion is shown originating in lobular masses, and in the section it is of a slightly 

 darker shade than the myeloid substance of the procerebrum. The antennal nerve is well devel- 

 oped. In a nearly horizontal section farther down (Fig. 3) the right olfactory lobe was cut 

 through on one side, where it is separated at this point by a stratum of ganglion cells. The 

 origin of the antennal nerve (ant. n.) is also well shown. The section also passed through the thick 

 commissure connecting the supra- and subcesophageal ganglia, and in the section forming a thick 

 ring around the oesophagus. 



The brain of Scoterpes. — It is now interesting to turn to the brain of Scoterpes (from Mammoth 

 Cave), which has even no traces of eyes, and study the modification to which the brain is subjected 

 as apparently the result of the total atrophy and disappearance of the eyes. The heads of two 

 specimens were each cut into fifty transverse sections. No traces of the optic ganglia, optic 

 nerves, or any part of the eyes, including the pigment of the retina or the corneal lenses, were 

 to be discovered. So far as these sections show, every trace of the organs of vision and the nerves 

 and ganglia supplying them are wanting in this genus. On the other hand, it may be remarked 

 that, so far as we have been able to see, the structure of the procerebral, olfactory, and commis- 

 sural lobes remain unaltered. As in all the other blind or eyeless forms examined, the supra- 

 cesophageal nerve-centers are not affected by the loss of eyes. This is as we might expect, for, the 

 sense of smell being rendered more acute, the olfactory organs are somewhat hypertrophied to 

 compensate for the atrophy of the organs of vision. We should not expect the central portion of 

 the brain, that controlling and coordinating the movements of the antennas and other parts of 

 the body, to be materially modified. Hence, as seen in the sketches we have made of selected 

 sections, the brain is as large in the eyeless Scoterpes, the cortical stratum of ganglion cells as 

 thick, and the myeloid substance of each ganglion as perfectly developed as in the allied forms 

 with completely developed eyes. 



PL XXV, figs. 4 and 5 represent sections through the brain of one specimen, and Figs. 6 to 10 

 thinner sections through the brain of the other specimen. In all the sections the optic ganglia 

 were not to be found, and they evidently are atrophied, with no traces of any differentiation from 

 the -central procerebral lobes, unless the outer rounded portion of the upper or pro cerebral lobes 

 be the rudiments of the optic ganglia, which scarcely seems probable. 



* The lithographer has scarcely done justice to the author's drawings for Plates XXIV and XXV, having shaded 

 parts left blank, and not having clearly brought out the eyes. 



t Ueber das unicorneale Tracheaten- und speciell das Arachuoideen- und Myriopoden-Auge. Von V. Graber. 

 Arohiv fur mikr. Anat., Bd. XVII, Heft 1, 58, Taf. VI, fig. 20. 



I Grenacher's Ueber die Augen einiger Myriopoden. Archiv fiir mikr. Anat., Bd. XVII, Heft 4, 415, Taf. XXI. 

 fig. U. 



