266 ANNUAL OF SCIENTIFIC DISCOVERY. 



the cumulative effect of natural selection or survival of the strong- 

 est; and that the views of Darwin well illustrate how large a part 

 the need of protection has pla,yed in producing" many of the most 

 striking peculiarities in the animal kingdom. The few exceptions 

 to the above law can in most cases be explained by the peculiar 

 habits of the species. 



[The same law holds good in the N. American birds.] Editor. 



ON THE LUMINOSITY OF THE SEA. 



Mr. Collingwood, in the " Quarterly Journal of Science," Oc- 

 tober, 1867, classes all the cases of luminosity which came under 

 his observation, during a voyage of eighteen months' duration in 

 temperate and tropical seas of both hemispheres, under the fol- 

 lowing five heads : 



1. Sparks or points of light, very common, often veiy brilliant, 

 varying in size from a pin's head to a pea, apparently caused by 

 minute entomostracous crustaceans. 



2. A soft, usually greenish, phosphorescent effulgence, seen only 

 in calm weather, when a smooth sea is disturbed by a keel or oars ; 

 due to the presence of innumerable Noctilucce and to minute En- 

 tomostraca. 



3. Moon-shaped patches of steady white light, several inches in 

 diameter, generally seen in the wake of the ship, such as might be 



.given out by the umbrellas of Medusce, but in his opinion not pro- 

 duced by Acalephce, but by Ascidians of the genus Pyrosoma. 



4. Instantaneous recurrent flashes of light, very common, seen 

 when the night is dark and the sea smooth, occurring at a distance 

 from the path of the ship and at a considerable depth in the 

 water. These maybe produced by Ascidians (when undisturbed), 

 by small Medusce, and by Noctilucce. 



5. Milky sea, of rare occurrence, considered by him as owing 

 rather to ill-understood atmospheric or climatic influences, than to 

 any extraordinary number of luminous animals. It may some- 

 times be due to the general diffusion in the water of the slimy 

 substance in which the luminous property in many marine animals 

 seems to reside. 



The luminosity is most frequent and brightest in warm seas. 

 Fish swimming rapidly in water abounding in minute luminous 

 animals would produce an effect depending on the disturbance 

 of the luminous points in their passage. This luminosity has 

 sometimes erroneously been supposed to proceed from the fish. 



CRUSTACEAN PARASITISM. 



Prof. Verrill states (" American Journal Science," July, 1867), 

 that in a collection of about 90 specimens of a small sea-urchin 

 (Euryechinus imbecilis, Verrill) from the coast of Peru, not one 

 could be found in which the anal area and surrounding parts of 

 the upper side of the shell were not more or less irregularly dis- 

 torted or imperfect. An examination of the interior showed that 

 in each specimen a crab (Fabia Chilensis, Dana), allied to the com- 



