599 



the crystalline cone and is secreted by the retinophorae on either side, 

 and hence the closely approximate cells in reality belong to different 

 ommatidia. The retinal cells now become greatly elongate and from 

 the retinophorae is formed the at first slender pedicel (rhabdom, Gre- 

 nacher) exactly as is claimed by Patten (1. c.) Pigment is first depo- 

 sited in cells 4, next in cells 1, and later in the intervening ones which 

 never become so deeply pigmented as the two just specified. 



All of the important parts of the eye are now outlined and the 

 subsequent development is quite regular. With the increase in size of 

 the crystalline cone the nuclei of the retinophorae and the correspond- 

 ing ones of the epidermis (which] secrete the cuticular lenses) are 

 forced to a position on the ends of the cone, while by the same process 

 the pigment cells are forced backward and form a sheath around the 

 style and pedicel of their respective ommatidia. From the ganglionic 

 layer nerves grow outward and penetrate the retinal elements, proceed- 

 ing even into the crystalline cone. In short my studies so far as they 

 go confirm the observations of P atte n as to the structure of the eye of 

 the adult Decapod and warrant his criticisms on the account of Gre - 

 na eh er. It merely needs to be said that I have not traced the fine 

 nerve terminations described by Patten as existing in the crystalline 

 cone. After hatching, the mesoblast in the optic cavity becomes devel- 

 oped into a thick layer of connective tissue in which there is an abun- 

 dant deposition of pigment. 



There is nothing in the development of the eye which warrants 

 the assumption that it or its stalk is an appendage homodynamous with 

 the other arthropod appendages ; and further, the development of a 

 compound eye from a single invaginated pit shows that it is not to be 

 regarded as derived from a coalescence of ocelli. 



Whether vali dor not the comparison instituted by L o c y ^ between 

 the eyes of Arthropods and those of Vertebrates is extremely interesting, 

 and the studies of Patten on the nerve terminations make them ever 

 more so. In the light of the facts here presented they do not appear 

 so absurd as they would have seemed a year ago. In both, the retinal 

 elements, with regard to their origin have exactly the same relation to 

 direction of the light ; there is an analogy in the nerve supply while 

 Patten's investigations on the nerve terminations show still another 

 point of similarity. I hope later, to show that the analogies (homolo- 

 gies ?) are even closer than the foregoing would indicate. 



As to a question of priority. Bobretzky was the first to describe 



2 Bulletin Mus. Comp. Zool. XII, p. 94, 1886. 



3 3an. KicE. 06. Ecx., Ill, T. I., 1873. 



