THE MITOTIC CYCLE 



are known; the clearest of which has recently been described by 

 Cleveland^"* in the very large chromosomes of flagellates parasitic in 

 termites, where an elastic thread 5-iOfj. long connects chromosome and 

 centromere (Figure 31). In Coccids there is no locaHzed point of 

 spindle attachment (Hughes-Schrader and Ris^^^) ; this diffuse 

 condition is characteristic of the Hemiptera in general. 



The chromosomes are surrounded by a sheath of material of different 

 composition, which in some instances appears to contain lipoproteins 

 (Hirschler;!*'^ Serra^"''). Probably the sister chromatids are thereby 



a-h late telophase, after cytoplasmic division, a centromeres of both chromosomes 

 attached to existing centriole which is hnked to the 4th flagellar band. A new 

 centriole is growing out from the 5th band; b astral rays from new and old 

 centrioles about to join and form central spindle of new achromatic figure; 

 c central spindle formed; d-h centrioles move to parallel positions as achromatic 

 figure develops and spindle becomes more rigid ; d lower right centromere has 

 shifted its connection from old to new centriole. i-j Prophase. Centromeres dupli- 

 cated and one from each group moves, k-m growth and function of achromatic 

 figure; k metaphase; I anaphase; m early telophase, before cytoplasmic division. 



Figure 31 The achromatic figure oi Holomastigotoides tusitala, and its connection with 

 the spiral flagellar bands. From ClevelandI"^ ^^y courtesy. Trans. Amer. Phil. Soc.) . 



kept together before anaphase (Metz^"^^) ; Schrader^'** ^^° has found 

 that interzonal connections in early anaphase are an extension of this 

 chromosome sheath. 



Suitably stained preparations of large chromosomes show coiled 

 filaments within, the chromonemata, set in an apparently homogenous 

 material, the matrix, the appearance of which around the chromosome 

 thread is sometimes the first event within the nucleus in early prophase. 

 Probably the composition of the matrix is variable (KLaufman^^^). 

 Some authors look upon most of the Feulgen-positive material deposited 

 on the chromosomes during prophase as belonging to the matrix; 

 Serra^"' speaks of this as the 'peripheric nucleo-proteins'. In the 

 salivary chromosomes of the Drosophila larva, there is evidence of a 

 difference between the proteins of the chromonemata and of the 

 matrix (p 103). It is believed by Kuwada^^^ that in Tradescantia changes 



92 



