5 8 KINGSLEY. [Vol. I 



to the development of the brain, and did not recognize its con- 

 nection with the retinal elements. 



The observations of Sedgwick and Kennel upon the develop- 

 ment of the eye in Peripatus may be referred to in this connec- 

 tion, although the present author does not believe this form to 

 be an arthropod. Sedgwick {^8^, p. 461) first described the 

 eye as arising by an invagination, and says that the outer wall 

 of the vesicle forms the epithelium outside the lens, while the 

 inner, from which the retina arises, remains continuous with the 

 cerebral ganglion, and hence the eye of Peripatus is a " cerebral 

 eye," an expression the force of which I fail to perceive. 

 Kennel, not quite a year later, gives an account of the develop- 

 ment of the eye in the two South American species studied by 

 him, illustrating it with three figures. i^86, pp. 3 1-33, and 83, PI. 

 iii., Figs. 32-34.) The account agrees essentially with that of 

 Sedgwick, except that Kennel maintains that the inner wall of the 

 vesicle is converted into only the retinal elements, and that it 

 does not unite with the cerebral ganglion until a late date. The 

 eye of Peripatus, as was first shown by Balfour ('(?/, p. 395, 

 and '8j, PI. xvii., Fig. 24) is totally unlike that of any arthropod. 

 Balfour compares it with the eyes of molluscs, but a far more 

 perfect parallel is to be found in the eyes of the Syllid worm 

 Autolytus. In this genus sections show an almost exact reproduc- 

 tion of Balfour's figure, cited above, except that the nuclei of the 

 ganglionic layer are visible all the way around the pigment until 

 they merge in the prelenticular epithelium of the optic vesicle 

 (Kennel's Fig. 34 shows a similar relation), and except that the 

 layer of rods and cones in the eye of Peripatus is represented 

 as divided by transverse bars or partitions which I cannot recog- 

 nize in the eye of the worm. In Autolytus the region between 

 the lens and the pigment is occupied by crystalline slightly 

 staining bodies, in the centre of which the nerve-fibre can be 

 traced, much as is represented in Patten's figure (/, ^,) 142. 

 These crystalline cones abut directly upon the spherical lami- 

 nated lens. 



To Locy (^86) is due the credit of first recognizing the 

 existence of an invagination in the development of the arthropod 

 eye. In the Arachnid Agelena he finds that both the median 

 and the lateral eyes originate by an invagination, and, excepting 

 the inner of the three resulting layers, the subsequent processes, 



