ZOOGENESIS 



to season, and at different hours of the day and night. 

 It is always constant in the sea. 



These physical variables on the land, which are 

 much reduced in importance and almost or even 

 wholly absent in the sea, create an infinite number of 

 different combinations each of which must be met by 

 a special complex of defensive or protective adapta- 

 tions in the land living animals. Not only that, they 

 must also be met through adaptations by all land 

 living plants as well. These adaptations on the part 

 of land living plants affect all the animals that feed 

 on them, but especially the insects which feed upon 

 all parts of plants. Diversity among plant feeding 

 insects means a corresponding diversity among their 

 parasites and the creatures feeding on them. 



The enormous diversity of conditions on the land, 

 both in regard to physical conditions of environment 

 and to food supply, is reflected in the diversity of all 

 land living types of animals, but particularly of the 

 insects which, because of their small size, are able to 

 penetrate into almost every economic niche. 



Zoology abounds with apparent paradoxes. In 

 spite of the great difference between conditions on the 

 land and conditions in the sea the dominant animal 

 types are the same both on the land and in the sea. 

 These are the backboned animals or vertebrates, the 

 arthropods or jointed footed animals — insects, spiders, 

 crustaceans and their allies — the mollusks, and the 

 jointed worms or annelids. These, with the pro- 

 tozoans and the nematodes (fig. 8i, p. i6i), are the 

 most successful and most widely spread of all animal 



