NUCLEI AND KINETIC ELEMENTS 121 



pact mass of chromatin spins out into an elongated reticulum from 

 which about 150 double chromosomes are formed by transverse 

 segmentation. These are divided longitudinally during the transi- 

 tion from the characteristic "crescent" to the full spindle figure 

 (Fig. 206, p. 496). Dehorne (1920) on the other hand maintains 

 that only one long, convoluted skein of chromatin is formed and 

 divided as such, therefore no chromosomes at all are in Paramecium. 



The division figure of Noctiluca miliaris is quite different from 

 the others of this group. The chromatin, according to observations 

 of Ischikawa and of Calkins (1895), is contained in a number of 

 large endosomes (chromatin reservoirs), each of which breaks up 

 into a mass of chromomeres. These collect in chromosome strings, 

 ("chromospires") which are oriented toward one pole of the nucleus 

 and are far too numerous to count. After division of the centrosphere, 

 the nucleus elongates and bends around the connecting centrodes- 

 mose in such a manner that the chromosomes form an incomplete 

 annular nuclear plate between which and the centrodesmose, the 

 nuclear membrane is absorbed. IVIantle fibers, attached to the ends 

 of the chromosomes, focus in a centriole in each daughter sphere, and 

 with the separation of the daughter centers, each chromosome is 

 longitudinally divided (Fig. 52, p. 101). 



A more definite Metazoon type of chromosome formation is 

 shown by the organisms comprising the second group above. Here 

 the number of chromosomes is usually smaller and their individual 

 history during nuclear division is less difficult to make out. A good 

 example, typical of the plymastigote flagellates, is Trichonympha 

 camyanella, as described by Kofoid and Swezy. Here the resting 

 nucleus contains a large granular endosome. In the prophase of 

 division the granules of this endosome give off chromatin along 

 the walls of the linin reticulum until a definite skein stage results 

 (Fig. 51, p. 100). Double chromosomes, 26 in number, and formed 

 by the splitting of the spireme segments, make up a definite nuclear 

 plate. They are attached by intranuclear fibers to the daughter 

 blepharoplasts and are divided longitudinally with the division 

 of the nucleus. The original connecting fibrils between the sep- 

 arating halves of the blepharoplast ("centroblepharoplast") remain 

 at all times outside the nuclear membrane, hence it is called a 

 paradesmose by Kofoid and Swezy (see Noctiluca). One of the 

 chromosomes appears to be different from the others, both in 

 resting and division stages, and is called the heterochromosome, 

 although its function or significance is quite unknown. Similar 

 odd chromosomes are known in some Gregarinidae and Coccidiida 

 where the vegetative stages are haploid, as well as in other poly- 

 mastigote flagellates. Except for the complications brought in 

 by the extensive neuromotor apparatus of Trichonympha cam- 

 imnella, the division figures of other, related, flagellates are quite 



