The Behavior of Centrioles and the Structure and Formation of the Achromatic Figure

Included among the many preparations for cell dtivision in mos,t higher plants and animals is the constel1ation . of eV'eruts encompassing the for mation . of the ,spindle or mitotic app'al'latus, depending upon th,e org1anism. These are transient structures, resP. onsible primarily fQr the equip'armtion of the heredi,tarY material, which 'are elabol'lated by cells jusrt in advance of division and d~sapp,ear from vi,ew shortly after ('and s. omemmes befol'le) the completion of dliviision. Pre6sely'What the . origin and fate of the structural molecules ,of the division figure may be is ,apparently not known. In con trast to ,the dear,th of factual tinformation in tbi,s regal'ld, an exterusive li. t era!ture describing the microscopically vilSihle ,aspects of mitotic apparatus build-up and break-down exists. Recently inv,estig,atioIliS of a more chemical nature inquil1ing into the chemical events associated wi,th mitotic 'appal'a,trus appearance and dis,app'eamnce have been reported. Whatever the under lying IScheme may be, it seems likely that ,the formation of the divis,ion figure involves complex ill'tel'laotiorus between IStructur. al mooeties that can he detected by light and electron micmscopy, their structural precursors and functional molecules. At the zenith of . its structul'lal development (mmally metaphase) the mitotic apparatus is an impressively complex ,and highly ordered structure. Usually it is in a ,state of continoOus change froOm the moment it first becomes bservwble until it oan no long,er be detected, although in some cells devdop ment may be arrested at metaphaise for weeks or mOll'ths.