60 BIOLOGY OF THE PROTOZOA 



Intranuclear Kinetic Elements. The kinetic elements, some of 

 which are intranuclear and a part of the fundamental organization, 

 are those structures of the cell which are closely connected with the 

 visible expression of the transformation of energy resulting from 

 destructive metabolism. Such expression may be in the form of 

 movement due to the activity of specific motile organs formed as a 

 rule from the substance of kinetic elements, or it may be in the form 

 of intracellular activities as indicated by the transformation and 

 movements of internal attraction centers, center of radiation, of 

 nuclear division, etc. The kinetic elements are justly regarded by 

 many observers as the most elusive and perplexing, but at the same 

 time amongst the most fascinating of all the organoids of Protozoa. 



Kinetic elements appear in Protozoa in a multitude of structures, 

 sometimes intranuclear, sometimes cytoplasmic, and often both 

 inside and outside the nucleus. Whether or not they are permanent 

 organoids of the cell is subject to the same arguments pro and con 

 which have been raised for and against the permanency of the cen- 

 trosome in Metazoa. There is strong evidence, as the following 

 pages will show, that not only are many types of cytoplasmic kinetic 

 elements derived from the nucleus, but also that chromatin and 

 intranuclear endobasal bodies are closely related, while some types 

 that are confined to the cytoplasm are composed in part, or entirely, 

 of a substance which closely resembles chromatin (parabasal bodies). 

 Little is known of the chemical composition of the latter, but both 

 intranuclear and cytoplasmic kinetic elements stain intensely with 

 some of the nuclear dyes and divide by simple constriction at 

 periods of cell division. 



In many cases it is impossible to tell from observations on ordi- 

 nary vegetative individuals, whether a given structure belongs to 

 the kinetic elements or to some other group of the many types of 

 protoplasmic granules. This is particularly true of the intranuclear 

 forms where incomplete extraction of a stain may give the appear- 

 ance of a granule in some chromatin or plastin mass. In such 

 cases the identity of the structure can be determined only by its 

 history during nuclear division. Cytoplasmic forms can be more 

 easily detected by reason of their relation to motile organs or to 

 more or less complex fibrillar structures. 



(«) Endobasal Bodies. — Pmdobasal bodies in nuclei of different 

 Protozoa are highly variable and no general description is possible. 

 In some cases they stain intensely with nuclear dyes, especially 

 with iron hematoxylin; in other cases they stain feebly or not at 

 all with the same dyes that color the chromatin (e. g., Chilodon). 

 In some cases they are large and appear homogeneous throughout; 

 in other cases there is a definite, deeply-staining central granule 

 embedded in a more faintly staining plastin (?) matrix, or such a 

 granule may be present without the accompanying matrix; or, 



