48 Jvdd—The Eye of Byhlis srrrafa. 



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

 Narragansett Bay with a tow-net at niglit. 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. 



S'l'RrCTlTKE OF THE EyE. 



Bijblis serntta possesses two pairs of crater-like eyes. One pair is a little 

 anterior to the other, and also somewhat nearer the sagittal i)lane of the 

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

 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 ej'es have a bright red appearance, owing to the presence of a large 

 amount of red jjigment surrounding the lens. 



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

 the chief axis. Beneath the thickened cuticula which constitutes tlie 

 single lens is the succession of cell layers and cell products, wliich 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 Bijblls, 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 ' Gammaridiv of the Gulf of Naples' appeared, con- 

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

 studied by Delia Yalle was Ainpelinca, a genus closely allied to Bi/ldis, 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 diff'er sbghtly in shape from those o£ Byhlis. Further, there is no 

 pigment in the hyi)odermis adjoining the lens. In the lentigen of J?»- 

 pelisca the nuclei are proi^ortionately much larger than in Byhlis, and the 



*A complete bibliography of the litei-ature 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. Mns. Comp. Zool., XXI, 

 1S91). The only recent histological paper on the eyes of anii)hipods of 

 the family Gaxitiiaridic is in Antonio Delia Valle's ' Gammarini del Golfo 

 di Napoli' (Fauna und Flora des Goifes von Neapel, XX, pp. lOS-ll'i, 

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



