﻿NORTH AMERICAN SPHINGlDiE. 105 



mediate forms by crossing, could be associated together for indefinite periods of time 

 in the same area, and hot have had the tendency called into activity long since, by 

 the production of permanent hybrids, now indistinguishable and registered as true 

 species. Hence, if there be anything of truth in a supposition so probable, it is easy 

 .to perceive why the hybrid is incapable of propagating with its own kind, and why 

 in mixing with the parent stock there is a constant tendency to revert to it. To 

 arrive at any satisfactory solution of the question, however, it will be necessary to de- 

 termine the effect of the intermixture of closely allied but distinct species from widely 

 separated countries. 



In order to make the foregoing ideas respecting species as clear and definite as possi- 

 ble, it may be well, perhaps, to throw them into the form of a definition. It may 

 be regarded, therefore, as a specific cycle of organic and instinctive actions, manifested in 

 the 'production of representative forms and in their biographies, having reference chiefly to 

 the continuance of special forms, these being unchangeable and immutable in all their essen- 

 tial characters, but variable in size and color. 



Species then, has an ideal existence in nature, and its representatives or the indi- 

 vidual in some of its forms, is that which falls under observation and with which the 

 naturalist deals in his generalizations. The description of species should be a biogra- 

 phy, and should present everything in the life of the group. It should commence 

 with the egg and give its form, markings and color ; its relations to the food plant ; 

 the means adopted for its security or protection. 



The young larva on emerging from the egg should be described, with its ornamenta- 

 tion and external structure or appearance; its metamorphoses or moltings, and the 

 successive changes produced in ornamentation and structure should be noted, until it 

 reaches the condition characteristic of maturity ; its habits, instincts and mode of 

 association with beings of its own kind observed ; its natural enemies and means of 

 defense, concealments or mode of self-protection ascertained ; its diseases described ; 

 the nature of its sustenance determined ; the physical conditions under which it lives 

 and its geographical range established. 



Its mode of preparing for pupation should be recorded, and whether the metamor- 

 phosis is immediate or delayed, and during what portion of the year it takes place ; 

 the pupa, its form and structure, should be described, and how the imago escapes from 

 the pupa case and cocoon. 



With the perfect insect should be given the number of broods during the year, 

 and the intervals of time during which the individuals of the brood appear, and the 

 months in which the imago may be met with ; its individual peculiarities of structure, 

 and the ornamentation of the normal form with the chief variations to which it is 

 liable. 



The determination of true species from the imago, is by no means simple or easy : 



