288 HALF HOURS WITH IN^SECTS. [Packard. 



same thought were taken up in successive geological periods, 

 and worked out in different ways, but with the same funda- 

 mental plan. The plan is the result of an unbroken line of 

 forms transmitted by genetic descent ; the variations in the 

 typical forms have been induced by changes in the soil and 

 air. These lines of development, from so-called archetypal 

 forms suddenly stop, and we have to follow them back before 

 we can again take up the thread of development of other 

 lines. There is not a continuous chain of being, but lines 

 of development sometimes parallel, but more often diverging 

 and connected by cross ties and branches linking the animal 

 creation into a whole, all converging to a primordial ances- 

 tor, perhaps no more highly organized than the structureless 

 Moner, a drop of living, moving, self-reproducing proto- 

 plasm. 



Turning now to the cases of mimicry in the butterflies 

 described by Messrs. Bates and Wallace and Trimen, from 

 South America, the East Indies and South Africa, respec- 

 tively, all agree that the Heliconidae are mimicked by other 

 butterflies which are ver^'- unlike the members of their own 

 families, and cop}^ in form and color the HeliconidiB which, 

 probably owing to a bad odor, are not eaten by birds, and 

 thus multiply in great abundance. The object of the mimic 

 is claimed to be a utilitarian one. It flies about in the dis- 

 guise of a Heliconia, and were it not for this protection it 

 and its offspring would become extinct. This resemblance, 

 moreover, has probably, these authors claim, been brought 

 about by natural and sexual selection. In the beginning 

 some butterfly, through the tendency to variation assumed 

 by Mr. Darwin, had a remote resemblance to a Heliconia ; 

 this favored it above its fellows, and the character growing 

 more strongly marked became perpetuated, until after a 

 great number of generations the similarity of form became 

 perfected. Mr. Darwin adopts the view, and regards the 

 mimicry as brought about by natural and sexual selection. 



32 



