ZOOGENESIS 



water. An amount of light sufficient to permit the 

 growth of any type of green or comparable plant ap- 

 pears to be sufficient for all, most, or at least some, 

 of the members of all the phyla or major groups of 

 animals. 



If we examine the major animal groups we discover 

 a very interesting fact. Broadly speaking their rela- 

 tionships to each other are very different from the 

 relationships between the major groups of plants. 

 The major groups of plants are in the main competi- 

 tive with each other, as they feed on the same sub- 

 stances in the same way. The existence of one or 

 another of these major groups, or if they occur to- 

 gether the balance between them, is largely deter- 

 mined by the amount of water and by the amount 

 and quality of the available light. 



The major groups of animals in their relation to 

 each other are on quite a different basis, for in the 

 main they are non-competitive, or perhaps it should 

 be said that they are fundamentally non-competitive. 

 While in their economic range the major groups, at 

 least the larger major groups, more or less overlap, 

 still there is always a certain section of their range 

 in which, as a result of differences in bodily structure, 

 they are safe from competition. 



The three largest and most important of the phyla 

 or major groups are the backboned animals or Verte- 

 brata, the jointed-legged animals or Arthropoda (in- 

 cluding the insects, centipedes, millepeds, spiders, 

 crustaceans, and their allies), and the mollusks 

 or Mollusca. 



