NUCLEI AND KINETIC ELEMENTS 103 



whereby amtrboid or flagellated buds are formed which contain a 

 nucleus derived from the parent cell nucleus, but no central grain. 

 This nucleus, however, contains an endobasal body wdiich divides 

 and one of the daughter granules emerges from the nucleus as it does 

 in Ndgleria gruberi (p. 86), but retains its centrodesmose for some 

 time and ultimately forms the central grain of the adult organism 

 (Schaudinn (1896), Zuelzer (1909), AcantJwcysiis aculeata, Wagner- 

 ella boreal is, Fig. 60). Similarity with the centroblepharoplast in 

 flagellates is thus shown (1) by its origin from an intranuclear 

 centriole; (2) by its relation to axial filaments which are homologous 

 with rhizoplasts; (3) by its history during mitosis. The analogy 

 is further strengthened by its relation to the flagella and to the 

 axiopodia which are simultaneously present in some of the Helio- 

 flagellida (Aciinomonas mirabilis, Kent, CiJiophrys marina, Caullery, 

 and Dimorpha mutaiis, Gruber). In Dimorpha mutans, the central 

 grain lies near one pole of the cell where it forms the basal body of 

 the two flagella as well as the focal point for the axial filaments, here 

 flagella and axial filaments appear to be homologous structin-es. 

 According to Zuelzer the pseudopodia of W agnerella borcalis are 

 withdrawn at times owing to the contraction of the entire complex 

 of radiating fibrils, and basal bodies lying at the bases of the axo- 

 podia become grouped in a zone of granules about the central grain. 

 When the pseudopodia are again formed the granules migrate centri- 

 fugally to the periphery and, as basal bodies, give rise to the axial 

 filaments. 



In Heliozoa without a central grain the axial filaments in some 

 cases center in the nucleus in which there are many distinct and 

 definite granules of uniform size distributed about the outer zone, 

 from each of which an axial filament appears to rise (Fig. 53, C). 

 In Camptonema nutans the nuclei are multiple, and, according to 

 Schaudinn, each one gives rise to a single pseudopodial element 

 (Fig. 53, A), but in ActinosphoEriiim eichhornii, which is also multi- 

 nucleate, the axial filaments apparently have no connection with 

 either nuclei or central kinetic elements. 



Apart from kinetic elements like centroblepharoplasts which, at 

 the same time, are centers of mitotic activity of the nucleus and of 

 kinetic activity of the motile organs, there are comparatively few 

 examples of kinetic elements comparable with centrosomes of Meta- 

 zoa. They are best represented in non-motile organisms such as 

 Sporozoa, whereas in freely -moving t^^^es there is always some pecu- 

 liar feature which makes the homology with centrosomes doubtful. 



The most frequently cited example of a centrosome in Protozoa 

 was first described by Hertwig in the case of AciinosphoBrium eich- 

 hornii (Fig. 64). Here, during the formation of the first matura- 

 tion spindle minute granules of chromatoid substance are cast out 

 of the nucleus and condensed into one or two minute centrioles from 



