NUCLEI AND KINETIC ELEMENTS 75 



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 

 iutranuclear 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 know^n of the chemical composition of the latter, but they 

 stain intensely with some of the nuclear dyes and divide by simple 

 constriction at periods of cell division. 



The kinetic elements vary in complexity from simple homogeneous 

 spheres and granules to extremely complicated systems of masses 

 and fibers, to which, in some cases, a sensory and conductile function 

 has been attributed in addition to the primary functions associated 

 with movements. To these more complex types Kofoid applies 

 the name "neuromotor" systems, a suggestive term first used by 

 Sharp (1914) in describing the characteristic structures and sup- 

 posed functions of the kinetic elements in Diphdinium ecaudatum. 

 In general, they appear to be more highly differentiated in parasitic 

 than in free-living types of Protozoa where, as Kofoid (1916) points 

 out, the denser media in which they live and have to move, such as 

 blood, mucus, intestinal contents, etc., require more powerful motile 

 organs and better developed kinetic centers than do water-dwelling 

 forms. On the other hand, free-living forms have not been so exten- 

 sively and carefully studied as the usually more minute parasitic 

 types and the field of investigation opened by the observations of 

 Yocom (1918) and the experiments of Taylor (1920) on Euplotes 

 patella indicate that free-living ciliates are not far behind in this 

 line of differentiation (see infra p. 109). 



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 l)y reason of their relation to motile organs or to 

 more or less complex fil)riHar structures. 



(o) Intranuclear Kinetic Elements (Endobasal Bodies). — Endobasal 

 bodies in nuclei of different Protozoa are highly variable and no 

 general description is possible. In some cases the}' stain intensely 



