February 17, 1905.] 



SCIENCE. 



267 



mosquitoes is the largest of the season be- 

 cause it contains the acciimulation of all 

 the eggs remaining unhatched for any rea- 

 son from the summer previous. Migrating 

 adults of this first brood live until Sep- 

 tember and the additions from later broods 

 give the impression of large summer broods, 

 whereas, in fact, the late broods are less 

 numerous than the earlier. 

 Light Organs of the Firefly, Photinus mar- 



ginellus: Anne B. Townsend, Friends 



Select School, Philadelphia. 



Investigations of physicists have shown 

 the light of the firefly to be the most per- 

 fect known ; not more than one one-thou- 

 sandth of the energy expended is converted 

 into heat. The nature of the process of 

 photogeny has not been conclusively de- 

 termined, although the theory which has 

 most credence is that the light is caused 

 by the oxidation, in alkaline media, of 

 some substance produced by the photo- 

 genic cells. Radziszewski has found carbon 

 compounds, similar to those found in living 

 organisms, which are luminous under siach 

 conditions. 



The purpose of the author's study has 

 been to find what light the structure of the 

 organs throws upon these theories. The 

 light organs of the male Photinus margin- 

 ellus are two plates lying directly upon the 

 hypodermis of the fifth and sixth abdom- 

 inal segments. These organs are made up 

 of two clearly defined layers : the dorsal, in 

 which the cells are filled with a dense con- 

 tent of opaque granules, and a transparent 

 ventral, the truly photogenic layer. With- 

 in the ventral layer the trachefe branch 

 profusely in an arborescent manner. The 

 vertical tracheal trunks with their branches 

 are surrounded by cylinders of transparent 

 tissue. Between the cylinders are paren- 

 chyma cells, irregular in size and outline, 

 and containing fine granules. At the pe- 

 riphery of the cylinders the trachefe send 

 out fine tracheoles, without chitinoi;s in- 



tima, which anastomose, thus forming a 

 close network of thin-walled air capillaries. 

 When fresh tissue is studied under a mi- 

 croscope in the dark room the light is 

 found to be uniformly distributed through 

 the area of this traeheolar network, the 

 cylinders appearing as non-luminous spots. 

 Crushed light organs placed in oxygen re- 

 spond instantly with increase of brilliancy. 

 The light extinguished by COj reappears 

 instantly when the tissue is placed in oxy- 

 gen. Experiments with a ctenophore, 

 Mnemiopsis leidyi, show similar results 

 with oxygen. Tissue in alkaline solutions 

 becomes brilliantly photogenic under the 

 influence of oxygen. The light is wholly 

 extinguished when tissue is placed in acid 

 solutions and does not reappear when oxy- 

 gen is introduced. When the acid solution 

 is made alkaline, the tissue again becomes 

 photogenic. 



Color Nomenclature: R. M. Strong, The 



University of Chicago. 



The color terms used in biology are 

 neither logical nor precise. An attempt to 

 reduce color terminology to something like 

 a precise system was made by Ridgway in 

 'A Nomenclature of Colors for Naturalists 

 * * *' (1886). This publication was use- 

 ful, particularly among ornithologists, in 

 securing more uniformity in the naming of 

 colors, but it employed the color terms in 

 common usage among artists, dye-makers, 

 etc. There is no general agreement con- 

 cerning the spectral positions of these col- 

 ors, and samples taken from various sources 

 show very great variations. 



The color system advocated by Milton 

 Bradley in his 'Elementary Color' (1895) 

 is both logical and precise. It is founded 

 upon six standards with definite spectral 

 positions. These are red, orange, yellow, 

 green, blue and violet. All other 'pure' 

 colors are obtained by combining these; 

 thus we get 'blue-green,' 'violet-red,' etc. 

 Diill or 'broken' colors and shades and 



