48 JuddTh<' A> nj' /;///>//* x 



R. I., during the summer of 1893, by skimming the surface of 

 Narragansett Bay with a tow-net at night. Various killing re 

 agents were tried, but the majority of specimens used and those 

 giving the best results were killed in Kleinenberg's picro-sul- 

 phuric acid. Sections were cut on a Minot- Zimmerman micro 

 tome and stained with Kleinenberg's hematoxylin diluted with 

 two parts of 70 per cent alcohol, and then decolorized in acid 

 alcohol for ten minutes. This work was done under the direc 

 tion of Dr. E. L. Mark, of Harvard University. 



STRUCTURE OF THE EYE. 



Byblis serrata possesses two pairs of crater-like eyes. One pair is a little 

 anterior to the other, and also somewhat nearer the sagittal plane of the 

 animal. The axis of the anterior pair makes a very acute angle with the 

 chief axis of the body, pointing forward and upward. The ventral pair 

 of eyes points downward and backward. In the living animal both pairs 

 of eyes have a bright red appearance, owing to the presence of a large 

 amount of red pigment surrounding the lens. 



The component parts of the eye are best seen in sections passing through 

 the chief axis. Beneath the thickened cuticula which constitutes the 

 single lens is the succession of cell layers and cell products, which col 

 lectively form a roughly spherical mass, connected at its deep end by 

 nerve fibers With the optic ganglia. Unlike the eyes of most Crustacea, 

 which are the type known as compound eyes, in which clusters of cells 

 called omatidia, acting independently of one another, are provided each 

 with its own proportion of modified cuticula, the eyes of Byblis, although 

 composed of clusters of cells, in some ways comparable with omatidia, 

 nevertheless have but a single lens, so that they have a superficial resem 

 blance to the eyes of spiders and other arachnids. 



After I had studied this new and peculiar type of eye in detail, Delia 

 Valle's paper* on the'Gammaridx of the Gulf of Naples' appeared, con 

 taining a figure and description of this same type of eye. The amphipod 

 studied by Delia Valle was Ampelisca, a genus closely allied to Byblis, but 

 the author had not been able to resolve the omatidium into its separate 

 elements. In Ampelisca, as shown by Delia Valle's figure, the rods and 

 cones differ slightly in shape from those of Byblis. Further, there is no 

 pigment in the hypodermis adjoining the lens. In the lentigen of Am 

 pelisca the nuclei are proportionately much larger than in Byblis, and the 



*A complete bibliography of the literature on the eyes of amphipods 

 will be found at the end of Dr. G. H. Parker's masterly paper entitled 

 'The Compound Eyes in Crustaceans' (Bull. Mus. Comp. Zool., XXT, 

 1891). The only recent histological paper on the eyes of amphipods of 

 the family Gammaridx is in Antonio Delia Valle's ' Gammariiii del Golfo 

 di Napoli' (Fauna und Flora des Golfes von Neapel, XX, pp. 108-112, 

 Tav. 46, Figs. 4-6, 1893). 



