DERIVED ORGANIZATION 107 



1. Blepharoplast, Basal Body and Centriole.— In many of the 

 comparatively simple Protozoa which have no specialized motile 

 organoids, the cytoplasm apparently lacks all traces of specific 

 kinetic elements. Thus in the entire group of Sporozoa, in the 

 simpler Gymnamebida and in testate forms of rhizopods, kinetic 

 elements, if present at all, are in the form of endobasal bodies within 

 the nucleus or as centrosomes close to it. Arndt (1924), however, 

 described a centrosome, with centriole, which divides and forms 

 the poles of the mitotic figure in Hartmannella Mitzkei, a testate 

 rhizopod (Fig. 58). In some of the relatively simple rhizopods, 

 however, especially those belonging to the family which Doflein 

 has called the Bistadiidae, from the fact that two distinct phases 

 an ameboid and a flagellate phase— are interchangeable, we find 

 organisms which throw light on the origin of cytoplasmic- kinetic 

 elements. Such dimorphic types of rhizopods have been repeatedly 

 observed since Dujardin first called attention to them, but details 

 concerning the origin of kinetic elements and the flagellum have 

 been made out only through use of modern cytological methods. 



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

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

 indicating their origin from an intranuclear kinetic element (Fig. 

 59,^4), 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. 59, B). 

 In the phytoflagellate Polytoma uvella, according to Geza Entz 

 (1918), the relation 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 rhizoplast with the nucleus. 

 In young individuals, however, the original single blepharoplast 

 (= basal body) is connected 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 different 

 points. The inference might be drawn in all such cases that the 

 cytoplasmic body represents one of the daughter halves formed by 

 division of the nuclear endobasal body, while the connecting fibril 

 represents the rhizoplast formed during such division. Such stages 

 are well illustrated by the dimorphic forms of rhizopods during the 

 transition from the ameboid to the flagellated phase. Thus Whit- 

 more described 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 Trimastig amoeba philipijinensis , and 

 Puschkarew described a similar condition in Dimasiigamoeha bista- 

 dialis (Fig. 59, C). The most complete observations, however, were 

 made by Charlie Wilson in connection with the transition from ame- 

 boid to flagellated stage in a closely-related form, Dimastig amoeba 



