82 Edmund B. Wilson 



sometimes be seen. The idiochromosome, on the other hand, 

 retains its identity and deep color and now appears as a conspicu- 

 ous elongated body ("caterpillar stage"). Though its outlines 

 are still somewhat ragged and its color less intense than in 

 the succeeding stages, it already appears in sharp contrast to 

 the pale reticulum (Photos 34 and 35). It sometimes extends 

 straight across the whole diameter of the nucleus; but beside such 

 forms, in the same cysts, are often curved and shorter forms. 

 At this time it is usually surrounded by a distinct clear space or 

 vacuole, as I hope the photographs may show; and there are also 

 in the nucleus from one to three much smaller nucleolus-like bodies 

 which (on account of the staining reactions) I believe to be plas- 

 mosomes, but these soon disappear. Splendid pictures of these 

 and the following stages are given by the safranin-lichtgriin 

 combination, which shows the idiochromosome at every stage 

 bright red, while in properly differentiated preparations the reticu- 

 lum is pure green. 7 The idiochromosome now takes up a pe- 

 ripheral position and the clear space surrounding it disappears. 

 It acquires a more definite contour, stains still more intensely, 

 and rapidly shortens until it is converted into a condensed ovoidal 

 or spheroidal chromosome nucleolus that may be traced without 

 a break through every stage up to the prophases of the first sperma- 

 tocyte division. As it shortens it may undergo a variety of form 

 changes. In what I regard as the typical process it shows no 

 indication of duality at any period up to the full contraction phase 

 (synizesis) being progressively reduced to a short rod and finally 

 to an ovoidal or spheroidal body (Photos 36 to 42). In the mean- 

 time the nuclear reticulum contracts more and more, usually 

 towards one side of the nucleus, becomes coarser in texture, and 

 increases in staining capacity, until at the climax of the process 



7 The effect of this stain depends in some measure, of course, on the relative degree of extraction of 

 the two dyes. My method is to stain in safranin for two to four hours and then to place the slide at 

 once in strong alcoholic solution of lichtgriin for ten to twenty seconds. This is at once followed by 

 rapid washing in 95 per cent and absolute alcohols. The alcohol is then replaced by clove oil and the 

 latter by xylol. In all cases the chromosomes of dividing cells and the chromosome nucleolus of all 

 stages appear brilliant red, the achromatic fibers and general cytoplasm pure green. The relative 

 intensity of red and green depend on the length of immersion in the green solution. The description 

 here given applies to sections rather strongly stained in the green. 



