No. 6. — Photomechanical Changes in the Retinal Pigment Cells of 
Palemonetes, and their Relation to the Central Nervous System. 
By G. H. PARKER.! 
CoNTENTS. 
Page Page 
Introduction . . 275) 6. Summary of Changes in Nor- 
Structure of the Eye in Palamonetes 276 THe Rinn 4. Se, » 05 
Photomechanical Changes in Nor- Sympathetic Photomechanical 
wal Net“ 28 CHAR 9S, ENS. 280 
er las heey 278 | Localized Photomechanical Changes 290 
2. General Changes in Retina . 279| Photomechanical Changes in Ex- 
3. Changes in Proximal Retinu- cised Eyes and Retinas . . . 291 
lär Golls s- . * . e . . 210 | General Summary, «. vo» 0. r 200 
4 Changes in Accessory Celle”. 281 Note 29097 
5. Changes in Distal Retinular Papers Cited 771 de 
Cells. . . . 284| Explanation of Plate. 
INTRODUCTION. 
THE present paper is a record of a series of experiments on the photo- 
mechanical changes in the pigment cells of the retina in Palemonetes 
vulgaris Stimp. This species is especially favorable for such work, 
since its retina exhibits in a marked degree all the kinds of pigment 
changes that have thus far been observed in the eyes of crustaceans. 
Those that have worked upon this subject have, in the main, fol- 
lowed in the lines laid down by Boll, Engelmann, and others in their 
studies on the eyes of vertebrates. Although the pigment changes in 
vertebrates are relativoly simple, they are, even now, far from being 
satisfactorily understood, and it is therefore not surprising that in 
the arthropods, where the pigment changes of the retina are probably 
more complex than in any other group of animals, much still remains 
to be done. There has been a tendency, moreover, among some of 
those that have studied such phenomena, to generalize on observations 
taken from eyes of totally different types, such as the compound eyes 
of insects and the simple eyes of arachnids; and this tendency, though 
1 Contributions from the Zoólogical Laboratory of the Museum of Comparative 
Zoology at Harvard College, E. L. Mark, Director, No. LXXVI. 
VOL, XXX. — NO. 6. 1 
