THE EVIDENCE FROM DEVELOPMENT. 



247 



life, but may take origin from stages in development prior to the full 

 period of growth. 



Given an ultimate independence of the young form, together 

 with the power of producing beings resembling itself, and we may 

 readily conjecture how a new and very different species or race may, 

 in comparatively rapid fashion, originate from a well-known stock. 

 Mr. Darwin gives as an example of this possibility, the case of the 

 beetle Sitaris (Fig. 165 F), of which the first larvae (A) are active 

 and minute, and possess six legs, two long feelers, and four eyes. 

 " These larvae are hatched in the nests of bees ; and when the male 

 bees emerge from their burrows in the spring, which they do before 

 the females, the larvae spring on them, and afterwards crawl on to 

 the females whilst paired with the males." Then ensues the laying of 

 eggs on the surface of the honey in the cells by the female bees, the 



FIG. 165. SITARIS AND ITS DEVELOPMENT. 



Sitaris larvae devouring the eggs. Then the latter undergo a meta- 

 morphosis. The eyes disappear, and the legs and feelers become 

 rudimentary (B), whilst they feed on the honey. At this stage they 

 more closely resemble ordinary insect larvae (C, D, E), and after further 

 transformation emerge as the perfect beetles (F). " Now," adds Mr. 

 Darwin, "if an insect, undergoing transformations like those of the 

 Sitaris, were to become the progenitor of a whole new class of insects, 

 the course of development of the new class would be widely different 

 from that of our existing insects ; and the first .'arval stage certainly 

 would not represent the former condition of any adult and ancient 

 form." " We can see," adds Darwin, " how, by changes of structure 

 in the young, in conformity with changed habits of life, together with 

 inheritance at corresponding ages, animals might come to pass 

 through stages of development perfectly distinct from the primordial 



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