November 3, 1905.] 



SCIENCE. 



,559 



to any principle of utility. Adaptation is 

 evident enough, but each species is as well 

 fitted for its life as any other, and no trans- 

 position or change of the distinctive specific 

 > characters or any set of them would in any 

 conceivable degree reduce this adaptation. 

 No one can say that any one of the actual 

 distinctive characters or any combination 

 of them enables their possessors to survive 

 in larger numbers than would otherwise be 

 the case. One or two of these traits, as 

 objects of sexual selection or as recognition 

 marks, have a hypothetical value, but their 

 utility in these regards is slight or uncer- 

 tain. It is customary at present to look 

 with disfavor on sexual selection as a fac- 

 tor in the evolution of ornamental struc- 

 tures, and the psychological reality of 

 recognition marks is yet unproved, though 

 not at all improbable. 



It may be noted, in passing, that the 

 prevalent dull yellowish and olivaceous 

 hues of the female orioles of all species is 

 clearly of the nature of protective colora- 

 tion. 



Professor "Vernon L. Kellogg has shown 

 statistically that certain specific characters 

 among insects have no relation to the proc- 

 ess of selection. Among honey bees the 

 variation in venation of the wings and in 

 the number and character of the wing 

 hooks is just as great when the bees first 

 come from their cells as in a series of indi- 

 viduals long exposed to the struggle for 

 existence. 



Among ladybird beetles of one species 

 {Hippodamia convergens) 84 different 

 easily describable 'aberrations' or varia- 

 tions in the number and arrangement of 

 the black spots on the wing covers have 

 been traced. These variations are again 

 just as numerous in individuals exposed 

 to the struggle for life as in those just 

 escaped from the pupal state. In these 

 characters there is, therefore, no rigorous 



choice due to natural selection. Such spe- 

 cific characters, without individual utility, 

 may be classed as indifferent, so far as 

 natural selection is concerned, and the great 

 mass of specific characters actually used 

 in systematic classification are thus indif- 

 ferent. 



And what is true in the case of the ori- 

 oles is true as a broad proposition of the 

 related species which constitutes any one 

 of the genera of animals or plants. All 

 that survive are well fitted to live, each 

 individual, and therefore each species fitted 

 to its surroundings as the dough is to the 

 pan, or the river to its bed, but all adapta- 

 tion lying apparently within a range of the 

 greatest variety in non-essentials. Adapta- 

 tion is the work of natural selection : the 

 division of forms into species is the result 

 of existence under new and diverse con- 

 ditions. 



To the general rule that closely allied 

 • species do not live together there exist 

 partial exceptions. It may be well to 

 glance at some of these, for no rule is es- 

 tablished until its exceptions are brought 

 into harmony with the phenomena which 

 illustrate the rule. 



The most striking case of this sort known 

 to us is that of the Pescado Blanco of the 

 volcanic lakes of Mexico, these constituting 

 the genus Chirostoma in the family of 

 Atherinidae. 



In the large lake of Chapala in central 

 Mexico, tributary to the Rio Lerma, one 

 species, Chirostoma estor, has been known 

 for years. It is a pale, translucent fish .of 

 elongate form, about fifteen inches in 

 length, with very delicate flesh, and it is 

 much appreciated as a food fish under the 

 local name of ' Pescado Blanco de Chapala. ' 

 In a recent visit to that region, the Pescado 

 Blanco was found to be abundant in the 

 lake, but to the great surprise of the writer, 

 in the same catch of the net were found 



