NUCLEI AND KINETIC ELEMENTS 87 



the family which Doflein has called the Bistadiidse, from the fact 

 that two distinct phases— an amoeboid and a flagellate phase— are 

 interchangeable, we find organisms which throw light on the origin 

 of cytoplasmic kinetic elements. Such dimorphic types of rhizo- 

 pods have been repeatedly observed since Dujardin first called 

 attention to them, but details concerning the origin of kinetic ele- 

 ments and the flagellum have been made out only through use of 

 modern cytological methods. 



In some Protozoa, e. g., Codosiga hotrytis, the kinetic elements of 

 the flagellum grow directly out of an endobasal body in the nucleus, 

 indicating their origin from an intranuclear kinetic element (Fig. 

 42, A), in other simple forms the flagellum arises from a kinetic 

 element situated in the cytoplasm but connected with the intra- 

 nuclear kinetic element by a rhizoplast at some stage (Fig. 42, B). 

 In Polytoma uvella according to Geza Entz (1918), the relations 

 between intranuclear and cytoplasmic kinetic elements varies with 

 the age of the cell. The usual condition in adult cells is two basal 

 bodies, one at the base of each flagellum, and neither of them is 

 connected by a rhizoi)last with the nucleus. In young individuals, 

 however, the original single blepharoplast (= basal body) is con- 

 nected by a rhizoplast with an intranuclear endobasal body, or a 

 larger rhizoplast from the blepharoplast may break up into a calyx 

 of fibrils which enter the nucleus at dift'erent points. The inference 

 might be drawn in all such cases that the cytoplasmic body repre- 

 sents one of the daughter hah'es formed by division of the nuclear 

 endobasal body, while the connecting fibril represents the rhizoplast 

 formed during such division. These stages are well illustrated by 

 the tlimorphic forms of rhizopods during the transition from the 

 amcpboid to the flagellated phase. Thus Whitmore describes a 

 cytoplasmic kinetic element functioning as a basal body which is 

 connected by a fibril with the nucleus and which lies at the base of 

 the flagella in Trimastigamoeba ijhili'p'pinensis , and Puschkarew 

 described a similar condition in Ndgleria inmdata (Fig. 42). The 

 most complete obser\ations, however, were made by Charlie Wilson 

 in connection with the transition from amoeboid to flagellated stage 

 in a closely-related form, Ndgleria gruberi, one of the soil amoebae. 

 She describes the nucleus of this organism as containing a typical 

 endosome within which an endobasal body is embedded. At the 

 period of flagellation this endobasal body divides and one daughter 

 element migrates through the substance of the endosome and 

 through the nucleus to the cytoplasm, retaining its connection 

 throughout with the intranuclear kinetic element (Fig. 42, C). In 

 the cytoplasm it becomes a basal body which gives rise to the kinetic 

 elements of the flagella. In these cases the extruded kinetic ele- 

 ment combines the functional characteristics of a blepharoplast and 

 a basal body or group of basal bodies. In this dual capacity it 



