158 BIOLOGY FOR BEGINNERS 



nervous systems becoming very efficient. In some there are found 

 eyes and other sense organs. 



The arthropods, which include the lobster and crab, all insects, 

 and spiders, constitute an enormous and highly specialized group 

 whose adaptations we shall study in detail. Then at the top of the 

 list come the vertebrates, including all backboned animals, fish, 

 frog, snake, bird, cat, and man whose place at the head of the class 

 is due, as always, to the specialization and development of the 

 organ with the highest function, namely the brain, with its ability 

 to think and reason. 



All this increase in adaptation brings the animal in closer touch 

 with its surroundings or environment. The amoeba vaguely turns 

 toward food and moisture, contracts if disturbed or perhaps turns 

 away from strong light. As development progresses, response is 

 made to other outside forces (stimuli) and we have organs for 

 touch, taste, smell, hearing, and sight, all of which enable the 

 animal to adapt its life to its environment and by that means be- 

 come successful in the struggle for existence which goes on with 

 its neighbors. 



COLLATERAL READING 



General Zoology, Linville and Kelly, pp. 292-304; Animal Life, Jordan 

 and Kellogg, pp. 24-49; Animal Studies, Jordan, Kellogg and Heath, 

 pp. 33-42; Animal Life, Thompson, pp. 143-152; Comparative Zoology, 

 Kingsley, pp. 318-320; Elementary Zoology, Kellogg, pp. 57-63; Essentials 

 of Biology, Hunter, pp. 199-210. 



SUMMARY 



Protozoa (first animals), one celled. 

 Metazoa (animals further on), more than one celled. 

 1. Development. 



Plant and animal begin as single cells (sperm, ovule). 

 Stages of progress. 

 One cell. 



Two cells to many in mass (Pandorina). 

 Hollow mass of cells (Volvox). 

 In-folded, hollow form, three layers (Sponges). 

 All higher forms, tissues from these layers. 



