THOUGHTS ON SPECIES. 167 



chiefly to the continuance of special forms, these being un- 

 changeable and immutable in all their essential characters, 

 but variable in size and colour. 



Species, then, has an ideal existence in nature, and its 

 representatives, or the individual 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 biography, and should present everything in the life of 

 the group. It should commence with the egg and give its 

 form, markings and colour ; its relations to the food plant ; 

 the means adopted for its security or protection. 



The youno; larva, on emergino; from the eg^, should be 

 described, with its ornamentation and external structure or 

 appearance; its metamorphoses or moultings, and the suc- 

 cessive changes produced in ornamentation and structure, 

 should be noticed, 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 defence, concealments or mode of self-protection 

 ascertained ; its diseases described ; the nature of its sus- 

 tenance 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 metamorphosis 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 pecu- 



