THE ACHROMATIC FIGURE 



155 



Such facts, taken together with the frequent reports of the appearance 

 of a normal centrosome only after the aster has become partly developed, 

 suggest that the centrosome is a result of activity in this region rather 

 than its cause. Moreover, cases are on record in which bodies described 

 as centrosomes have turned out to be effects of microtechnical treatment. 

 Such an interpretation of the phenomena at mitotic centers in cleaving 

 animal eggs has recently been advanced by Fry (1928, 1929, 1932), 



Fig. 85. — First meiotic mitosis in the spermatocyte of Salamandra. I, prophase: 

 centrioles in centrosphere substance, which is spread out on nucleus. II, prophase: 

 bivalent chromosomes formed; centrioles beginning to diverge; central spindle and asters 

 developed. Ill, late prophase: nuclear membrane gone; centrioles moving apart; "fibrils 

 attaching to chromosomes." IV, anaphase: connecting fibers prominent. V, telophase 

 cytokinesis by constriction nearly completed; mid-body forming at equator. (After 

 Meves, 1897.) 



but its general validity is strongly opposed by other observers.^ Centro- 

 somes have been seen in living spermatocytes (Johnson, Pollister, Belaf). 

 In animal cells the amphiastral figure commonly develops essentially 

 as follows. The centriole, with or without centrosphere substance, is 

 usually double as the result of a division during the course of the preceding 

 mitosis. As mitosis begins, the daughter centrioles begin to move apart, 

 and as they do so they are seen to be connected by a small "central 

 spindle." About each of them an aster develops (Fig. 85). The result- 



7 Wilson (19306), Pollister (1930, 1932), Belaf (1929c), Wilson and Huettner 

 (1931), H. H. Johnson (1931). 



