436 Journal of Comparative Ne^irology and Psychology. 



lights the eye by the excellence of its form and arrangement, and 

 rejoices the heart with the thoroughness and accuracy of the work and 

 the far-reaching importance of its results. It is really a continuation 

 and amplification of the investigation by the same authors on "Hippo- 

 lyte varians : a study in color-change"/ extending the observations 

 made on this species and including a study of Cra/igoii. Palaemon, 

 Carcinus, Portunits and Galathca. based upon Macronixsis as a funda- 

 mental type. 



In Macyo»iysis the authors observe that the color units, the chro- 

 matophores, are arranged in three main groups and one accessory 

 group. The three main groups are (i) the neural, in relation to the 

 brain and nerve-cord ; (2) the visceral, connected with the alimentary 

 tract, liver and gonad ; (3) the caudal group ou the upper surface of 

 the tail. These three groups are so related that they may be conceived 

 as forming a system, the primary system of chromaiophorcs. The acces- 

 sory group, on the other hand, is related to outlying structures, and 

 may be considered as an incipient accessory system. The chromato- 

 phores are not simple cells, as they are widely considered, but consist 

 of a protoplasmic, pigmented center, enclosed in a spherical thin-walled 

 bag, which is pierced by the proximal ends of a number of cells vary- 

 ing from five to nine. These cells have their nuclei in, or close to, the 

 chromatophore center, and extend outward in branched, fibrillated 

 processes, the whole being not unlike the branching of a tree. 8ome 

 of these branches are 2 mm. and over in length. 



The chromatophore centers of Macromysis contain two kinds of 

 pigments, a brown pigment, which turns red and is finally decolorized 

 under the influence of oxydizing agents, and a small quantity of pig- 

 ment which is bright yellow or white by reflected light, but has a gray- 

 ish color in transmitted light. It is the brown pigment that gives the 

 characteristic color pattern to the animals, giving them a dark brown 

 tint when expanded, i. e., when the pigment migrates to the branches, 

 and leaving them colorless or gray when the pigment contracts to the 

 center. 



In decapod Crustacea the situation is much more complex. The 

 color-marking of the adult decapod is determined by the development 

 of the secondary system of chromatophores, which completely covers 

 \i\) the first and differs from it in having much shorter branchings 

 and being much more decentralized. In the larval stages, however, 

 through the Mysis stage, the primary system remains in the ascend- 



' Keeble, Frederick, and Gamble, F. W. Hippolyte varians: a Study in 

 Color-change. Quart. Joiirn. Micros. Science, Vol. 43, pp. 5S9-698, 1900. 



