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l6 K'lXG. [Vol. X\'II. 



eggs taken from the body cavity, and these chromosomes must 

 be derived from the twelve chromatin rings which were found 

 in connection with the first polar spindle before its migra- 

 tion to the periphery (PI. XXIX, Figs. 25-27). One of the 

 twelve groups of chromosomes found in eggs from the body 

 cavity must, therefore, be equivalent to one of the chromatin 

 rings of the earlier stage. Unfortunately I have not a com- 

 plete series of preparations showing all of the transitional 

 stages from Figs. 25, 26, 27 to Fig. 28 ; yet it maybe of inter- 

 est to trace as closely as possible the changes occurring during 

 this period. After the twelve chromatin rings have reached 

 the spindle, they split longitudinally (Figs. 26, 27), so that 

 there are twenty-four chromosomes in the form of closed rings. 

 Each ring then separates into two parts at its thickened por- 

 tion, and thus forty-eight half-rings are formed, each ending in 

 knob-like thickenings. This second separation of each ring 

 into two parts is not a transverse division, but merely a break- 

 ing apart of the chromatin threads which originally fused to 

 form the ring. During the migration of the spindle towards 

 the periphery, a concentration of the chromatin material must 

 take place, as the chromosomes found on the spindle after the 

 periphery is reached are very much smaller than those at the 

 stage of Fig. 28. Besides this concentration, there is also an 

 apparent decrease in the number of chromosomes, as there are 

 but twelve groups or twenty-four chromosomes to be counted 

 in the equatorial plate of the spindle in eggs taken from the 

 body cavity (PI. XXX, Figs. 30, 31). Each of these chromo- 

 somes must, therefore, be equivalent to one-half of a chromatin 

 ring before it underwent longitudinal division at the stage of 

 PI. XXIX, Fig. 26; that is, it must represent one of the two 

 original chromosomes from the germinal vesicle which fused 

 to form the ring. The apparent lessening of the number of 

 chromosomes from forty-eight to twenty-four might be brought 

 about in two ways : either the two sister portions of one-half a 

 chromatin ring which were completely separated in an earlier 

 stage (Fig. 26) have fused again, or they lie so close together 

 that it is impossible to distinguish between them. These 

 changes must take place verv soon after the stage of Fig. 26, 



