104 BIOLOaV OF THE PROTOZOA 



which fibrillar structures radiate into the cytoplasm and throughout 

 the nucleus. This structure, however, has no permanent relation 

 to the cytoplasm or nucleus, but disappears after the first maturation 

 spindle is formed while subsecjuent maturation spindles and spindles 

 of division stages are characterized by pole plate formation (see 

 p. 81). Much more typical centrosomes are found by Arndt (1924) 

 in HartmmmeUa (PsemhchJamys) klii::Jcei (Fig. 41, p. 85) and in the 

 Gregarinida, especially in the Monocystis types where they have been 

 described by Leger, Brasil, ]\Iulsow, Doflein and others. In 

 Monocy.siis roslrafa, for example, a single centrosome with marked 

 astral radiations, lies outside the nuclear membrane (P'ig. 63). 

 An amphiaster is formed as in egg cells of Metazoa, and a complete 

 mitotic figure results. Similar centrosomes occur in Urosyora 

 lagidls St. (Umospora varia, Leger and Stylorhynchus longicoUis, St. 



Transitory centrioles and centrospheres are present in Noctiluca 

 miliaris Sur. In resting stages there is no evidence of the cen- 

 trioles while the centrosphere disappears in the granular mass of 

 endoplasm. In the early stages of cell division, however, the cen- 

 trosphere condenses into a fairly homogeneous cytoplasmic mass of 

 large size outside the nucleus. This divides into two daughter 

 spheres connected by a fibrillar centrodesmose, while centrioles of 

 unknown derivation appear in each sphere and are connected by 

 mantle-fibers with the ends of the chromosomes (Fig. 52). 



The very peculiar Xebenkern of the rhizopod Paramoeba eilhardi 

 as described by Schaudinn and the "nucleus secundus" of P. 

 pigmentifera and P. chcpfognathi as described by Janicki, are less 

 easily homologized with centrosomes. They have nothing to do 

 with the nucleus during division nor with motile organs, but, as 

 Doflein hints, may be interpreted as parasites from their appearance 

 in Janicki's figures. 



In general we do not find the same types of kinetic elements in 

 Infusoria that are found in other forms of Protozoa. Blepharo- 

 plasts, parabasal bodies and centrosomes are still unknown in 

 ciliates, although certain peculiar kinetic elements are present here 

 which may turn out to be homologous with one or more of these 

 structures. Endobasal bodies, howe\er, are known in micronuclei 

 of a few types (e. g., Urolepius mobUis, O.ryfricha faJJa.v, and in some 

 macronuclei (e. g., Chilodon cumiUus, Fig. .34, p. 77). On the other 

 hand, certain special types of cytoplasmic kinetic elements such as 

 myonemes, motorium, and conductile fibers, are characteristic of 

 the ciliates some of which become highly complicated coordinated 

 neuromotor elements. 



The most widely distributed of the kinetic elements are the basal 

 granules of the cilia, which are situated in the contractile zone of 

 the cortex (see p. 144). The exact nature of these extremely minute 

 bodies is unknown and their origin or renewal is purely hypothetical. 



