160 PROTOZOOLOGY 



long as the old one, the centrioles begin to produce astral rays (b) 

 which soon meet and form the central spindle (c). An astral ray from 

 the new centriole becomes connected with the centromere of one of 

 the chromosomes (d). The spindle grows in length and enters resting 

 stage (e-j), later the spindle fibers lengthen (k, /) and pull apart (m). 



The chromosome is composed of the matrix and chromonema 

 (Fig. 63), of which the former disintegrates in the telophase and re- 

 appears in the early prophase of each chromosome generation, while 

 the latter remains throughout. From late prophase to mid-telophase, 

 minor coils are incorporated in major coils (a-c) ; from mid-telophase 

 to late telophase, they are in very loose majors (d); and after the 

 majors have disappeared completely, they become free (e). Soon 

 after cytoplasmic division, the majors become looser and irregular 

 and finally disappear, while minors and twisting remain. Each chro- 

 mosome presently divides into 2 chromatids (f) and a new matrix is 

 formed for each. As the matrix contracts the chromatids lose their 

 relational coiling and the minors become bent and thus the new 

 generation of major coils makes its appearance (g). With the further 

 concentration of the matrix, the majors become more conspicuous 

 (h), the minors being incorporated into them. When most of the re- 

 lational coiling has been lost and majors are close together, the 

 chromosomal changes cease for days or weeks. This is the late pro- 

 phase. After the resting stage, the achromatic figure commences to 

 grow again (i, j) and the two groups of chromatids are carried to the 

 poles, followed by transverse cytoplasmic division (Fig. 64). The 

 coils remain nearly the same during metaphase to early telophase. 

 Thus Cleveland showed the continuity of chromosomes from genera- 

 tion to generation. He finds that the resting stage of chromosomes 

 varies in different types of cells: some chromosomes rest in inter- 

 phase, some in early prophase and others in telophase, and that the 

 centromere is an important structure associated with the movement 

 of chromatids and in the reduction of chromosomes in meiosis. For 

 fuller information the reader is referred to the profusely illustrated 

 original paper (Cleveland, 1949). 



In Lophomonas blattarum, the nuclear division (Fig. 65) is initiated 

 by the migration of the nucleus out of the calyx. On the nuclear 

 membrane is attached the centriole which probably originates in the 

 blepharoplast ring; the centriole divides and the desmose which 

 grows, now stains very deeply, the centrioles becoming more con- 

 spicuous in the anaphase when new flagella develop from them. 

 Chromatin granules become larger and form a spireme, from which 



