IV PREFACE 



present in fundamental form in spores, cysts and eggs. Each such 

 oi"ganization under appropriate stimuli undergoes differentiation 

 through which the derived or visible organization is developed from 

 the fundamental organization. Through irritability' of protoplasm 

 and reactions to internal stimuli arising through metabolic activities 

 as well as through reactions to external stimuli, the fundamental 

 organization is progressively changed. Such changes lead to 

 reproduction by division whereby the changed organization is 

 restored to the fundamental t^'pe. Other changes are cumulative 

 and lead to special modifications of organization which we recognize 

 as meiotic, gametic and zygotic phenomena, with accompanying 

 processes of reorganization and restoration to the fundamental 

 organization. Reorganization thus may be accomplished by divi- 

 sion alone (for example animal flagellates) by parthenogenesis 

 (endomixis in ciliates) , or by fertilization phenomena. Such changes 

 are cyclical in character and differ from other changes in funda- 

 mental organization (variation) which may be induced by permanent 

 change in external environment, or by changed stimuli resulting 

 from modifications of the germ plasm. 



This conception is fully developed in the following pages. The 

 various t^'pes of visible organizations which form the basis of classi- 

 fication are described and keys are introduced to aid in the placing 

 of the more common genera. The fundamental vital f mictions are 

 treated as manifestations of vitality. Life and vitality are treated 

 as independent concepts— life as organization, and vitality as the 

 activity of the organization. The various phases of vitality —youth, 

 maturity, and old age— are consequences of changed or changing 

 organization through continued metabolism. Death is disintegra- 

 tion of the organization. 



To many friends and colleagues who have helped in the prepara- 

 tion of this work I wish to express my grateful appreciation. The 

 illustrations, testify to the artistic skill of many different assistants, 

 among whom I am particularly indebted to INIiss Mabel L. Hedge 

 (frontispiece and others), Mr. B. Manson Valentine, Mrs. Martha 

 Clark Bennett and Miss R. Bowling. To the publishers, finally, I 

 want to express my thanks and appreciation for their patience and 

 good nature in waiting for a work long overdue, and for their coopera- 

 tion and interest in the making of the book. 



Gary N. Calkins. 



Columbia University, 1926. 



