December 27, 1901.] 



SCIENCE. 



999 



tinental, and not American trains. As a matter 

 of fact, this pressure has little effect on the or- 

 ganisms inhabiting the depths on account of 

 their being themselves so largely composed of 

 and permeated by sea water. But the release 

 of pressure experienced by individuals sud- 

 denly transferred from deep to shallow water 

 is most disastrous in its effects, as illustrated 

 by the fate of deep-water fishes when brought 

 to the surface. 



In discussing the chemical composition of sea 

 water the author states that the oxygen is de- 

 rived from the atmosphere, and that the car- 

 bonic acid increases with the depth, and that 

 this latter fact explains the lighter calcareous 

 skeletons of deep-sea forms as compared with 

 their shallow-water relatives. On the other 

 hand, silicious skeletons from great depths are 

 proportionately heavier than those from shal- 

 low water, although actually smaller. In this 

 connection the point might well be raised that 

 the heavier calcareous skeletons are not needed 

 in the depths for weight or protection against 

 waves or currents, and that their comparative 

 fragility could be accounted for on other grounds 

 than the solvent action of carbonic acid. 



The problem of the penetration of sunlight 

 is treated at considerable length. This subject 

 has been made a matter of investigation by 

 means of experiments with sunken photo- 

 graphic plates, the greatest depth at which 

 even the most sensitive are in any degree 

 affected being 500 to 550 m., according to Fol 

 and Sarasin. Red rays, however, might still 

 be present without affecting the photographic 

 plates, and the reddish yellow twilight of 

 Agassiz and Haeckel might result. 



Professor Seeliger denies the red-light the- 

 ory, and maintains that the blue or blue-green 

 rays penetrate most deeply. He substantiates 

 his argument by an ingenious reference to the 

 well-known and beautiful illumination of the 

 famous ' Blue Grotto ' of Capri, where the light 

 penetrates a considerable depth of sea water 

 and is reflected upward into the cave. Spec- 

 troscopic investigation confirms this blue-light 

 theory, which appears to be now well estab- 

 lished by the arguments here recorded. The 

 author believes that no light from the sun 

 reaches the greater depths, and says that no 



conditions of existence in the deep sea have so 

 strongly influenced the organization and manner 

 of life of animals as the absence of sunlight 

 and heat. 



The coloration of deep-water forms is re- 

 garded as protective in the main. In explana- 

 tion of the red color so often found, the claim 

 is made that this color would be protective, on 

 account of its being inconspicuous in a blue 

 light. This point is debatable, in the opinion 

 of the reviewer, as any neutral tint would be 

 just as inconspicuous as red, and thus the ut- 

 terly useless production of such quantities of 

 bright pigment be avoided. After noting the 

 frequency of dark-colored or black hues among 

 the abyssal fishes, and the contrast between 

 this rich pigmentation, on the one hand, and the 

 bleached, often colorless condition of cave ani- 

 mals on the other, the author fails to grasp 

 the significance of the contrast. He doubts the 

 effective presence of attractive coloration as an 

 aid to sexual selection in the deep ' wo die tiere 

 gar nicht oder nur unvollkommen sehen ' (sic !). 

 Indeed the discussion of the coloration of deep- 

 sea forms is the most unsatisfactory part of the 

 work. 



The loss of sight in abyssal animals is fre- 

 quently compensated for by the special devel- 

 opment of other organs, usually tactile, such 

 as the extremely elongated spines of certain 

 fishes, the immensely lengthened antennae of 

 crustaceans such as Nematocarcinus gracilipes 

 and Sergestes magnificus. Such structures are 

 often coordinated with degenerate eyes. Sense 

 hairs are sometimes greatly developed in deep- 

 sea annelids and on the lengthened legs of cer- 

 tain crabs. 



The author claims that a light, aside from 

 that of the sun, is found in the depths in the 

 form of phosphorescence, and this he discusses 

 in a very interesting manner. The fisherman 

 at night draws up his net filled with ' tausenden 

 gliihender Fiinckchen.' The light-emitting 

 forms increase in the deeper waters, " Hier fin- 

 den sich zeitlebens festgeheftet am Meeres- 

 grund lebhaft phosphorescierende Rindenkoral- 

 len, stark blaulich leuchtende Seefedern. Hier 

 leben zahlreiche leuchtende Wiirmer und Proto- 

 zoen, prachtig gliihende Seesterne {Brisinga) 

 und Cephalopoden." 



