NUCLEAR DIVISION IN PROTOZOA. 229 



manently in this diffused condition, as Strasburger practically 

 postulates in his kinoplasm theory. In plants, however, no cen- 

 trosphere is formed, the spindle fibers alone representing the 

 archoplasm. The increasing diffusion of the substance of the 

 sphere (archoplasm) explains the variations in the mitotic figures 

 as given at the outset of this chapter, the central spindle gradu- 

 ally becoming fainter and fainter in a series of forms, until it 

 finally is lost. It also explains a number of anomalous cases, 

 such as the formation of asters in poisoned echinoderm eggs, 

 described by Hertwig, ' or the artificial asters recorded by 

 Morgan. 



The mantle fibers, or fibers which connect the kinetic cen- 

 ters and the chromosomes, also have an archoplasmic origin, 

 and are primarily nuclear in position. In this primitive con- 

 dition they are seen in Actinospharium (Gruber, Hertwig, 

 Brauer), in Euglypha (Schewiakoff), in Spirochona (Biitschli, 

 Plate, Hertwig, Balbiani), and in micronuclei (Hertwig, Mau- 

 pas). In all of these cases they run from pole to pole, or from 

 pole plate to pole plate. With the extranuclear position of the 

 kinetic center, the rupture of the nuclear membrane becomes 

 necessary, for only then can the union of central spindle and 

 mantle fibers take place. With this in mind the controversy 

 over the nuclear or cytoplasmic origin of mantle fibers gains an 

 added interest ; for in either case they are formed from the 

 same substance, which may be either nuclear or cytoplasmic 

 in position. 



A comparison, I believe, may be drawn between chromatin 

 and archoplasm. In its earliest form the chromatin is massed 

 in one or several large reservoirs, which later break down into 

 granules distributed throughout the nucleus. The granules 

 may be permanent or temporary, but in all cases they come 

 together again as chromosomes. Similarly, archoplasm, in its 

 primitive form, is a single mass which becomes diffused through- 

 out the nucleus and cytoplasm, but in all cases comes together 

 again in the form of spheres or spindle fibers. As chromatin 

 is considered a definite substance or modification of protoplasm, 

 so also may archoplasm be regarded in the same light. 



The centrosome question, finally, is made no clearer by study 



