ZOOGENESIS 'P^" 



tural range from the tadpole or the leptocephalid to 

 the highest mammal is scarcely greater than the 

 structural range found in certain individual species 

 of crustaceans or of insects at different stages in their 

 development from newly hatched young to adults. 



Thus v^hile in many animal types wc are able to 

 trace, as in the horses, a gradual evolution from a 

 form which is simple and generalized in structure to a 

 group of forms all of which are highly specialized, 

 this is by no means always true. Indeed, it is the 

 exception rather than the rule. All lines are broken 

 by gaps which may be small and insignificant, or 

 broad and striking. 



It is commonly assumed that these various gaps are 

 due to our lack of adequate knowledge of the animals 

 concerned, and especially of their fossil record. No 

 doubt in many cases this is partly, or even perhaps 

 largely, true, but in very many cases these gaps un- 

 doubtedly are real and never were bridged by so-called 

 missing links. 



In the light of our present knowledge it is not pos- 

 sible for us to doubt that all living things are the chil- 

 dren of other living things, and that life has been 

 continuous from parent to child from its earliest 

 beginnings. How is it possible to harmonize this 

 fact with the occurrence of broad and unbridged gaps 

 in the evolutionary lines? 



The answer is that continuity of life does not neces- - 

 sarily imply a similar continuity of the bodily form \ 

 in which that life is manifested. In other words, 

 children may be very different from their parents. As 



