and Laboratory Methods. 1541 



the first ganglion these bundles break up into constitutional bundles. This 

 ganglion, like the eye, is made up of two halves connected by a thick bunch of 

 vertical nerve fibers. The ganglia are complex. An especially important 

 element is the granular layer, containing darkly staining bodies, " nerve nodes " 

 (Nervennoden), corresponding to the ommatidia in number. These consist of 

 neuroglia fibrils, which come from several ommatidia ; the fibrils do not end, but 

 pass on to other ganglia. As the fibers leave the first ganglion to pass on to the 

 •second, they cross so that the right becomes left and vice versa. The import- 

 ance of this crossing lies, according to the author, in the varying lengths of the 

 fibers, which have a physiological significance, explained as follows : Suppose 

 the eye to be stimulated in such a way that a certain set of retinulae receive an 

 equal impulse. These impulses pass down the fibrils to the second ganglion, 

 but owing to variation in the length of these fibers will arrive at different times. 

 If it is supposed that a stimulus affects one ommatidium only, a successive 

 series of changes in the nerve centers would follow, since each ommatidium has 

 seven nerve fibrils and each has a different length from the others. This theory 

 of arthropod vision was reached by the author by a process of induction, but he 

 believes he is supported by the theories of other authors who have based their 

 conclusions on theoretical grounds. a. m. c. 



CURRENT ZOOLOGICAL LITERATURE. 



Charles A. Kofoid. 



Books and separates of papers on zoological subjects should be sent for review to 

 Charles A. Kofoid, University of California, Berkeley, California. 



Seeliger, 0. Tierleben der Tiefsee. 49 pp., i This brief treatise on the abyssal life 

 Taf., Verlag von W. Engelmann, Leipzig, ^f ^.^g ^^^^^ ^^^^^^ ^^g subject in SUC- 

 1901. Preis Mk. 2. 



cinct fashion in the light of the latest 



investigations in this field of zoological exploration. A short historical sketch 



is followed by an explanation of the factors of the environment, such as the 



chemical condition, pressure, temperature, and light. The problems that center 



about the coloration, phosphorescence, and vision of deep-sea animals are also 



discussed. c. a. k. 



Nutting, C. C. The Hydroids of the Wood's Students at marine laboratories will 

 Hon Region. Bull. U. S. Fish Commission welcome Professor Nutting's paper on 



for I099, pp. 325-306. I9OI. o r r 



these favorite forms of seaside study. 

 The descriptions are brief, but illustrations, mainly original, are abundant, and 

 very full keys are provided for both hydroid and medusa stages. In all, 112 

 different forms are described from Wood's HoU and Newport indicating the 

 richness of the hydroid fauna in that region. In providing for the preparation 

 and publication of a series of papers, of which this is one, upon the local fauna 

 at the Wood's Holl Station, the United States Fish Commission is rendering 

 valuable aid to all American students of marine life. c. a. k. 



