APPENDIX: A SURVEY OF THE KINDS OF 



ORGANISMS 



This book deals with those broad aspects of life that help us to under- 

 stand man as an organism and to appreciate the various relationships 

 that exist among all forms of life, including man. In attempting thus to 

 treat of life in general, we have had to discuss many particular examples 

 and kinds of organisms, for "life" as such is a mere abstraction. There is 

 no life save in the form of real individuals that belong to particular species 

 and genera and higher groupings and that exist as members of actual 

 socioeconomic complexes. We are not especially concerned with the 

 classification of animals and plants, except to the extent that this classi- 

 fication enables us to see where our chosen examples stand in relation to 

 other forms of life. A survey such as that which follows does have another 

 value, however, in that it furnishes a panoramic view of the results of 

 organic evolution at its current stage. 



The background for this survey is contained in the preceding sections 

 of this book. In Part I we reviewed the major patterns of organization in 

 structure and function; classification is based largely upon knowledge of 

 comparative anatomy and physiology. In Part II we examined the 

 concept of heredity, upon which any taxonomic scheme based upon 

 relationship must rest. Part III showed how homologies in structure, 

 origin and function give a basis for judging relationship; it also reviewed 

 the geological evidence bearing on the evolution of plants and animals. 

 In Chap. XXIV the principles of classification and the methods of naming 

 organisms were discussed. 



Here we shall survey many of the actual patterns into which living 

 things have been molded by the process of evolution. The groups are 

 arranged as far as possible in phylogenetic order; of course, no sequential 

 treatment can fully express relationships. The most that can be done is to 

 try to keep closely related groups together and to place the simpler and 

 less specialized first, the more complex and more specialized later. These 

 two aims are mutually inconsistent when we pass from one group to the 

 next; we leave the highest forms of the first to take up the lowest forms 

 of the next, and often this means going from more complex back to 

 simpler organisms. 



This appendix is designed primarily for reference but should not on 

 that account be deemed unimportant. Knowledge of the principal groups 

 of plants and animals and their major subdivisions is essential to an under- 

 standing of much of the general content of biology. 



The accompanying chart is designed to show some of the more impor- 

 tant phylogenetic relationships within the plant and animal kingdoms, 

 and the structural levels of the various groups. It is necessarily very 

 much generalized, but it will aid in placing the groups treated in preceding 

 chapters and in the following pages. 



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