416 



considerably in extent. At this stage a large number of small, round, 

 feebly staining granules appear in or near the forming spindle. These 

 granules very soon fuse into 8 — 20 large irregular masses which take 

 a much deeper stain than the separate granules. 



After the reappearance of the chromatin, the spindle always Hes 

 near the black pole with its longitudinal axis parallel or slightly 

 oblique to the upper surface of the egg. The radiation from the 

 middle of the spindle gradually disappears and the spindle becomes 

 barrel shaped with well defined asters at each pole, some of the rays 

 from each aster crossing at the equator of the spindle. At no period 

 in the history of the first polar spindle in the egg of Bufo lentiginosus 

 have I been able to find centrosomes in the polar asters. As the 

 spindle gradually becomes more slender and pointed, the rays converge 

 more sharply at the poles and apparently run into each other in the 

 centre of the aster; but no method of fixation or staining has shown 

 the presence of any kind of a central corpuscle. 



Twelve irregular shaped chromosomes arise from the chromatin 

 masses scattered along the spindle fibres. These chromosomes soon 

 lengthen out into rod shaped structures which lie with their long axes 

 resting on the spindle fibre. Each chromosome then acquires a 

 rounded knob at each end and also one in the middle. The end 

 knobs later disappear, but the middle knob increases in size and 

 spreads out laterally on both sides of the chromosome forming two 

 wing -like projections which are raised up from the spindle fibres. 

 In proportion as the lateral arms grow, the polar arms decrease in 

 length and thickness, so that, soon after the chromosomes have 

 become arranged at the equator of the spindle, the lateral arms have 

 entirely absorbed the polar arms and each chromosome is a V shaped 

 structure with the angle of the V turned in towards the centre of the 

 spindle. 



During metakinesis the polar asters reach their greatest develop- 

 ment, and from this time on they gradually degenerate until there 

 is no longer any trace of them to be found. The spindle fibres then 

 converge to distinct points surrounded by a small accumulation of 

 granular substance, probably formed by disintegration of the rays. 



All of the chromosomes do not undergo the same changes simul- 

 taneously, as on the same spindle chromosomes of varying sizes and 

 in several difi'erent stages of development may be found. However, 

 when the chromosomes have become arranged at the equatorial 

 plate, they all appear to be of the same size and they are all 

 in the same stage of development with the polar arms very nearly 



