No. 2. — The Compound Eyes in Crustaceans. By G. H. Parker. 1 



Table of Contents. 



Page 



I. Introduction . 45 



II. The Retina ....... 47 



III. Arrangement of the Ommatidia 60 



IV. Structure of the Ommatidia . . 66 



1. In Amphipoda 68 



2. In Phyllopoda 73 



3. In Copepoda 77 



4. In Isopoda 84 



Page 



6. In Cumacea? 99 



7. In Schizopoda 99 



8. In Stomatopoda .... 104. 



9. In Decapoda 108 



V. Ommatidial Formulae . . .115 



VI. Innervation of the Retina . .116 



VII. Theoretic Conclusions . . .118 



VIII. Bibliography 131 



5. In Leptostraca 98 1 IX. Explanation of Figures . . .141 



Introduction. 



Some four years ago, at the suggestion of my instructor, Dr. E. L. 

 Mark, I began the investigation of the compound eyes in Crustaceans. 

 Iu order to familiarize myself with the subject, I determined to study 

 at first in detail the structure of th^ eyes in a single species, and for 

 this purpose I turned my attention to our common lobster, Homarus 

 americanus. My results were published in a paper entitled " The His- 

 tology and Development of the Eye in the Lobster." Since the publica- 

 tion of that paper, I have had the opportunity of examining the eyes in 

 a number of other Crustaceans, and my observations and conclusions 

 concerning these eyes are contained in the following pages. 



The material which I have used in the present study was in part sup- 

 plied to me through the kindness of several friends, and in part collected 

 by myself. Of that which I obtained myself, some was gathered in 

 the immediate vicinity of Cambridge, but much of it came either from 

 Wood's Hull, Mass., or from Newport, R. I. The material which I 

 obtained at Newport was collected at the Newport Marine Laboratory 

 during the summer of 1890, and consisted of specimens of Idotea, 

 Evadne, and Pontella ; that which I got at "Wood's Holl was collected 

 at the United States Fish Commission Station during a brief period 



1 Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology, under the direction of E. L. Mark, No. XXV. 

 vol. xxi. — no. 2. 



