938 THE AMERICAN NATURALIST. | [Vor. XXXV. 
Uca, while Homarus remains ; in the mollusk the latest vagaries of 
the systematist are introduced, while in the worms a more conserva- 
tive course has been adopted. Here and there errors occur. Thus 
the nemertines are regarded as a class of Plathelminthes, and (p. 164) 
the flatworms are stated to lack an anus. Under the Gephyrza, 
Sipunculus nudus is included as an American form, while Echiurus 
and Thalassema are ignored. Yet these are minor blemishes, and 
the work will prove most useful not only to the casual visitor to the 
shore but to the more experienced naturalist as well. K. 
PHYSIOLOGY. 
that Hydra viridis, when attached by the foot and placed in the path 
of a constant current of weak intensity, brings the long axis of the 
body in line with the current, the oral end being toward the anode. 
This orientation is accomplished by a contraction on the anode side 
of the body. When the animal is not attached by the foot, the anode 
side still remains the side of contraction, even though the oral end 
may be turned toward the cathode. In addition to orientation, the 
current may call forth general contractions. Separate pieces of the 
hydra react in much the same way as whole animals. Buds and 
parent animals are independent in their reactions, the buds showing 
essentially the same reactions as adults. P. 
Evolution of Pigment. — The interest which biologists have 
shown in the chemical activities of protoplasm has evinced itself in 
the study of pigment as a protoplasmic product. Bohn’s ? contribu- 
tion to this subject is a timely résumé of some of the more important 
recent results. The pigments are classified as hydrocarbons, deriva- 
tives of chromatin, and derivatives of the aromatic series. The 
vegetable pigments are described under the heads of chromogenic 
bacteria and chloroleucites. The occurrence, migration, and trans- 
formation of animal pigments occupies much of the volume. The 
author believes that in a given cell there may be a struggle between 
arl, R. The Reactions of E to the Constant Current, Amer. Journ. 
has vol. v (1901), pp. 301- 
2 
2 Bohn, G. L' Evolution du Pami Paris, Carré et Naud, 1901. 96 pP- 
