EUPAGURUS. 567 



Note on the Structure of the Eye. 



Since this Memoir was put in type, I have seen a 

 recent paper by Dr. E. Trojan on " Das Auge von 

 Palaemon squilla " (Denk. d. Math. Naturwiss. Klasse 

 d. K. Akad. d. Wiss. Wien, Bd. 88, 1912). 



The following are the most interesting points 

 in it : — He agrees with Parker that there are only 

 two corneal cells. They are broader distally than 

 proximally, so that they appear triangular in transverse 

 section. The crystalline cells are abruptly cone-shaped 

 distally, and pass between the corneal cells to the facet : 

 he confirms Parker in regard to their general structure. 



The general structure of the retinular cells and 

 rhabdome is as Parker and later writers have described, 

 but he supports Hesse's opinion (and differs from Parker 

 and Schneider) that there is no " zwischensubstanz " 

 between the " stiftchen " composing each half -plate of 

 the rhabdome. Three optic ganglia are described. 



The most important part of the paper is devoted to 

 a study of the pigment of the eye in darkness and light ; 

 this, however, is best consulted in the original. The 

 author states that there are only two pigment-bearing 

 cells, which form a continuous tubular sheath enclosing 

 the whole ommatidium, and believes this to be the case 

 for all Decapods. Parker's statement that the retinular 

 cells and tapetum (accessory) cells are pigmented, is, 

 therefore, possibly erroneous. The paper is illustrated 

 by most beautiful plates. 



