DERIVED ORGANIZATION 105 



have led to much confusion in terminology as well as in interpreta- 

 tion. Indeed the type of development of the kinetic elements in 

 flagellates is entirely different from that in ciliates and at the 

 present time, at least, they cannot be homologized. Any attempt, 

 therefore, to present a clear picture of the diverse elements and to 

 distinguish one type from another inevitably leads to contradictions 

 in interpretation. The facts may be marshalled, however, into 

 fairly logical series indicating increasing complexity in the organiza- 

 tion of the cell. Such series are presented in the following pages 

 with the understanding that they involve no claim of finality, nor 

 do they indicate phylogenetic relationships. 



The kinetic structures most frequently found in the cytoplasm 

 of Protozoa are relatively simple, the more complex types which 

 have been revealed being found in comparatively few cases. In 

 considering Protozoa as a group, therefore, too much weight should 

 not be attributed to these more complicated forms. For purely 

 descriptive purposes they may be considered in the following order: 

 (1) Kinetic elements, which are morphologically and functionally 

 equivalent to intranuclear centrioles forming parts of endobasal 

 bodies and usually derived from them ; (2) blepharoplasts equivalent 

 to basal bodies, or independent of basal bodies, which lie at or near 

 the bases of motile organoids and give rise to the kinetic structures 

 in them ; (3) basal bodies derived from and independent of blepharo- 

 plasts; (4) parabasal bodies which are closely connected with the 

 blepharoplasts and probably derived from them ; (5) centrodesmoses 

 and paradesmoses, or connecting fibrils between kinetic elements at 

 the spindle poles; ((>) rhizoplasts, or fibrils originating as outgrowths 

 from the substance of specific kinetic elements and connecting two 

 such elements or ending blindly in the vicinity of the nucleus; (7) 

 astrospheres and centrosomes, similar to analogous structures in 

 the cells of Metazoa; (8) miscellaneous kinetic elements such as 

 centroblepharoplasts, axostyles, parastyles and the neuromotor 

 apparatus of flagellates. An entirely different series involves the 

 motorium, conductile fibrils, and myonemes of Infusoria together 

 with the silver line systems of the ciliates which we have included 

 in the structures of the fundamental organization (see p. 80). 



Since many of these are characterized by their functional activi- 

 ties as well as by their specific structures, it is not illogical to find 

 that the same organoid performs generalized functions. Thus a 

 blepharoplast may be the same as a centriole, or as a basal body; 

 rhizoplasts may arise as a broken centrodesmose or paradesmose; 

 a myoneme as a conductile element, etc. The complexities of organi- 

 zation arise from the simultaneous presence of many of these differ- 

 ent kinetic elements in the cell where they may form a coordinating 

 system of organoids which Sharp and Kofoid have aptly designated 

 the neuromotor system. 



