52 KINGSLEY. [Vol. I. 



with the other appendages I see no reason to change the view 

 I have ahvays held that it is not. If it is we must allow all ar- 

 thropod eyes arising from invaginations {^e.g., spiders) to be ap- 

 pendages, and in this way we should find ourselves in no end of 

 trouble. In Astacus the eye attains the dignity of a stalk at a 

 very early date ; in Crangon, at the time of hatching, the con- 

 striction which is to make it a mobile organ has hardly be- 

 gun. Some remarks on this point will be found in my paper 

 on Limulus (^85, pp. 545, 546). 



Last in order I must refer to Patten's valuable paper (^86), 

 which has thrown a flood of light upon our knowledge of the ar- 

 thropod eye, and which, so far as I have tested it, is accurate in 

 all its details of structure. It treats, however, only of the adult ar- 

 thropod eye. Still it has some speculations which must be no- 

 ticed. Dr. Patten (/. c.^ p. 688) mentions the question as to an 

 invagination in the compound eye, and dismisses it with the re- 

 mark that, though possible, it is not proven, and further states 

 that the rods are not inverted. Still, on p. 680 he is driven to the 

 conclusion that the ancestral arthropod eyes consisted of closed 

 optic vesicles, formed by invaginations lying close beneath the 

 hypodermis, which formed a continuous layer over them. He 

 further constructs a figure (PI. xxxii.. Fig 141) to illustrate his 

 idea, but regards the deeper wall of the enclosed vesicle as 

 forming the layer of rods and cones, while the outer one either 

 disappears or forms the so-called vitreous body. In this he was 

 doubtless influenced by his belief that the layer of rods was not 

 inverted (and in this belief he was warranted as can be seen 

 from the foregoing review of the literature). Had he recognized 

 even the possibility of this inversion he would doubtless have 

 modified his theory and diagram. 



That the layer of cones is inverted was first pointed out by 

 Locy, and can readily be traced in the figures illustrating the 

 present paper. The deeper ends of the retinal structures touch 

 the optic cavity, which, of course, was primarily a portion of the 

 external surface of the body, while the outer or distal ends of 

 the retinophorae were primitively turned from the surface. This 

 fact has some weight, and Carriere ('6'<5, p. 499) is hardly war- 

 ranted in his criticism of Locy's comparison of the eye of a 

 spider with that of a veterbrate. In both the layer of rods and 

 cones is developed from the outer wall of an invaginated vesi- 



