260 BIOLOGY OF THE PROTOZOA 



furthermore, that such changes or differentiations from the funda- 

 mental organization underlie the phenomena of cell division, of 

 endomixis, of sex differentiations, fertilization and protoplasmic age 

 followed by natural death. In the following section an attempt is 

 made to correlate these characteristic phenomena in a life cycle 

 with progressive changes in the organization of the protoplasm. 



II. ORGANIZATION AND DIFFERENTIATION. 



It is evident to any one who has made a study of Protozoa that 

 forms and structures are practically unlimited. It is equally evi- 

 dent that these characteristics are specific for each species. Regen- 

 eration experiments show, furthermore, that these specific charac- 

 teristics are carried in all parts of the protoplasm of an individual, 

 a small part of a Stentor becomes a perfect Stentor, a small part 

 of a Uroleptus develops into a fully differentiated Uroleptus, etc. 

 The structure of the adult by which we recognize the species in 

 any particular case is the product of the finer make-up of the 

 protoplasm as it exists in a cyst for example or in a rounded-out 

 fragment cut from the body of an adult. What this finer make-up is 

 is purely conjectural, but the idea is carried by the non-committal 

 term "organization" as used in the preceding chapters. In this 

 term we include both the adult structures of the fully formed indi- 

 vidual and the undifferentiated protoplasm which has the ability to 

 produce them. There is reason to believe that the differentiations 

 which characterize the adult are brought about as a result of 

 metabolic activities constituting vitality, and these may be induced 

 by changes in environmental conditions as when an organism 

 emerges from a cyst, or regenerates at division periods (p. 221); or 

 they may require a longer period of metabolism and be combined 

 with growth; or they may appear only as a result of cumulative 

 differences representing a gradual change in organization. In gen- 

 eral the facts at hand warrant the statement that differentiations 

 always involve changes in organization, and for purposes of descrip- 

 tion it is convenient to describe them as: (1) Inter-divisional or 

 Ontogenetic Differentiations, and (2) Cyclical Differentiations. 



1. Inter-divisional Differentiations.— In the development of a 

 Metazoon differentiated structures are never present in the initial 

 egg cell but appear in orderly sequence as a result of metabolism, 

 growth and division of cells. A protozoon about to emerge from its 

 cyst is comparable with such an egg cell. The cyst wall becomes 

 permeable, water and oxygen are admitted and metabolism begins. 

 Soon the characteristic motile organs make their appearance differ- 

 entiated from the apparently homogeneous protoplasm. The oral 

 apparatus, anal aperture and contractile vacuole appear and the 



