Concurrence and Recapitulation 193 



stage of independent life being succeeded by the pupa or 

 chrysalis, which has a protected mode of life in which the 

 special adaptations of the later and more complex existence 

 are made ready. 1 This is a case in which the evolution 

 process has maintained the ancestral worm-stage intact. 



(2) In the development of eggs deposited with shells, 

 etc., and of uterine embryos, we find a device by which the 

 early stages are accomplished under special protection 

 without the independent early life seen in the cases of 

 species having larvae. 2 In the uterus all the environmental 

 conditions necessary to development are realized as in the 

 actual environment of ancestral forms, yet with varying 

 detail ; so that the internal uterine development is most 

 favourable for the exhibition of recapitulation. 



It is evident that embryological and such other modes 

 of life as that illustrated in the chrysalis have thus their 

 utility and ' reason for being ' ; for without them the 

 preservation of the mode of development leading up to 

 full heredity, as we find it, would be impossible, and so 

 would, as a consequence, the special evolution of this or 

 that species to its complex stage. The essential combina- 

 tion all along has been the accomplishment of progressive 

 heredity with the addition of new adaptations. Recapitu- 

 lation gives us a view of a former of these factors, the 

 mechanism of heredity ; concurrence shows us the oper- 



1 As this is being written, the extraordinary development of the seventeen- 

 year locusts is going on, thousands of these creatures coming, in the writer's 

 garden, from the earth, where their complete preparation for life has been 

 made. 



2 See the experimental proof that the shell of the egg is such a protection 

 to the development processes, by Weldon (research on the effect of intro- 

 ducing water, which, by promoting evaporation, hindered the development of 

 the amnion), in Biometrica, I. 3, p. 368. 



o 



