482 BIOLOGY OF THE PROTOZOA 



facts of the life cycle in Sporozoa; his work has been confirmed by 

 scores of investigators and upon an enormous number of representa- 

 tive species. A sequence of vital phenomena intervening from 

 fertilization to ultimate gamete formation and fertilization is 

 characteristic of all such cycles and in all cases the race comes to 

 an end with the formation of gametes, and without fertilization the 

 gametes die. Similar cycles are characteristic of Foraminifera 

 and wherever, gametes are formed the ultimate fate is the same. 

 With ciliates except in rare instances, gametes are not formed but 

 the organization of the protoplasm undergoes changes at maturity 

 when fertilization processes (conjugation) occur, and in the great 

 majority of pedigreed cultures, the race, like gametes, comes to an 

 end by natural death (see p. 552). The life cycle in all Protozoa 

 signifies the series of events between fertilization and fertilization 

 again or natural death. It involves characteristic changes in 

 organization of the protoplasm and equally characteristic manifesta- 

 tions of vitality. In the following section an attempt is made to 

 correlate these characteristic j^henomena in the life cycle with pro- 

 gressive 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 

 evident that these characteristics are specific for each species. 

 Regeneration experiments show, furthermore, that these specific 

 characteristics are carried in all parts of the protoplasm of an indi- 

 vidual, a small part of a Sfentor becomes a perfect Stenfor, a small 

 part of a Vroleptiis develops into a fully difl'erentiated Urolephis, 

 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- 

 \'idual and the undifl'erentiated protoplasm which has the ability 

 to produce them. There is reason to believe that the differentia- 

 tions 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. 484) ; 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 

 general the facts at hand warrant the statement that differentiations 



