1 897-] ENTOMOLOGICAL NEWS. 235 



place in nature Thus, certain lizards which live on the white 

 sands (great beds of gypsum) in New Mexico have assumed a 

 white color, which is doubtless protective. Similar lizards on 

 the adjacent sandy plains are pale brownish, which color is there 

 equally protective. Whiteness is not inherently superior to 

 brownness, but each has its advantages under certain conditions, 

 and the whiteness of the white lizards enables them to occupy a 

 territory not well suited for the brown ones. But there are many 

 characters on which the life of a species depends other than those 

 of color and form, which are visible in preserved examples. The 

 ability to subsist on particular kinds of food, to endure extremes 

 of heat or cold, of drought or moisture, to escape the ravages 

 of various diseases, cunning or swiftness to avoid particular ene- 

 mies, the peculiarity of appearing at a particular season of the 

 year. etc. ; all these powerfully affect the survival of the organism, 

 and therefore may become as true "specific characters" as any 

 of those usually employed for purposes of diagnosis. 



On theoretical grounds it does not appear necessary that all 

 distinct species should possess distinctive marks visible in pre- 

 served specimens. Most of them do possess such marks, for 

 reasons which need not now be discussed; but we might expect 

 to find some — perhaps many — lacking them, or only to be dis- 

 tinguished by very obscure characters. As a matter of fact, there 

 are many such cases, and it is to these I have applied the term 

 physiological species. Strictly speaking, all species are physio- 

 logical species, but the phrase, as applied to this particular class 

 of cases, is sufficiently suggestive and accurate. 



Entomologists should be on the lookout for physiological spe- 

 cies. They may differ in the time of appearance — as the 13-year 

 Cicada; or in the food-habits, as the Jamaican Aspidiotiis aurantii 

 which never infests the orange; or in the host, as certain bird- 

 lice: or in the voice — such cases are well known, at least among 

 birds ; or even in the odor or power of resisting a particular 

 disease. 



It may be asked, how are we to be assured that such forms 

 are species ? We may be so assured, I take it, if they are found 

 to live perfectly independent lives, never intermingling — that is, 

 the tests of specific validity are the same as in ordinary cases. 

 As a matter of fact, we may expect to find all sorts of gradations 

 between physiologically distinguished individuals, physiological 



