MUSEUM OF COMPARATIVE ZOOLOGY. 99 



had the opportunity of studying the eyes in Nebalia, I can offer it 

 merely by way of suggestion. 



Probably two kinds of accessory cells are present in Nebalia ; one of 

 these extends from the corneal cuticula to the basement membrane, the 

 other, the presence of which is not so fully established, probably occurs 

 near the basement membrane. 



Cumaceoe. 



Excepting what is contained in Burmester's ('83, pp. 35-37) account 

 of the degenerate eyes in Diastylis (Cuma) Rathkii, nothing, I believe, 

 is known of the finer structure of the eyes in the Cumacese. The speci- 

 mens at my disposal for the study of these eyes proved upon examina- 

 tion to be blind. At least, the optic plates of all the individuals which 

 I examined, both when studied from the exterior and when examined 

 in sections, showed no evidence of eyes. My material consisted of 

 specimens of Diastylis quadrispinosa, G. 0. Sars, and of three other un- 

 determined species, two of which belonged to the genus Diastylis and 

 one to Eudorella. These were kindly sent me by Prof. S. I. Smith. 



Schizopoda. 



The species of Schizopod the eyes of which T have studied is Mysis 

 steuolepis. Smith. Specimens of this Crustacean were kindly collected 

 for me at Wood's Holl, ]\Iass., by Mr. C. B. Davenport. I am also 

 under obligations to Dr. H. V. Wilson, of the United States Fish Com- 

 mission, who at my request sent me specimens of this species freshly 

 preserved in jSIiiller's fluid. 



In several of the previous accounts of the eye in Mysia the nuclei 

 of the corneal hypodermis, although recognized, have been described as 

 Semper's nuclei, i. e. as nuclei of the cone cells. The differences between 

 the hypodermal nuclei and those of the cone cells can be easily seen in 

 Mysis steuolepis (Plate YII. Fig. 73). In this species the hypodermal 

 nuclei {nl. crii.) lie in a plane somewhat nearer the external surface of 

 the eye than the nuclei of the cone cells (71L con.). In transverse sec- 

 tions at the proper levels, each ommatidium will be seen to contain two 

 elongated nuclei (Fig. 75, nl. crn.) belonging to the corneal hypodermis, 

 and two oval nuclei (Fig. 76, 71I. con.) in the cone. The hypodermal 

 nuclei occupy such positions that the plane of separation between their 

 cells would be at right angles to that between the cone cells (compare 

 Figs. 75 and 76). The group of four nuclei, two belonging to the corneal 



