74 Edmund B. Wilson 



Although I have no smear preparations of Syromastes it is perfectly 

 clear from the sections that the facts are the same here as in Anasa 

 Alydus, and other forms. In the early prophases of the first divi- 

 sion (at a period corresponding to Gross's Figs. 31 to 37) when the 

 plasmosome has disappeared or is greatly reduced in size, the 

 nuclei contain both the chromosome-nucleolus and the m-chro- 

 mosomes. This is shown in great numbers of cells with unmis- 

 takable clearness and after various methods of staining, particu- 

 larly after safranin alone or combined with lichtgriin. In the 

 early part of this period the chromosome nucleolus is at once 

 recognizable by its intense color and sharp contour and is not 

 for a moment to be confused with a plasmosome. The ordinary 

 bivalents are still in the form of ragged pale bodies, having the 

 form of longitudinally split rods or double crosses. The m-chro- 

 mosomes have the same texture and staining reaction, but are 

 much smaller and never show the cross form. While it is diffi- 

 cult to show the facts to demonstration in photographs of sections 

 they may be fairly well seen in the following. Photo 18 shows the 

 chromosome nucleolus (not quite in focus,) one of the large biva- 

 lents (two others barely appear) and both m-chromosomes. 

 Photo 19 is a similar view (the m-chromosomes more condensed), 

 while Photo 20 shows the m-chromosomes and three of the ordi- 

 nary bivalents. The succeeding changes must be rapidly passed 

 through, since the successive steps are often seen in the same cyst, 

 passing from one side to the other. In these stages the large 

 bivalents rapidly condense and regain their staining capacity, 

 finally assuming a bipartite or quadripartite form. The m-chro- 

 mosomes undergo a similar condensation, being finally reduced to 

 ovoidal or spheroidal bodies. The chromosome nucleolus, on 

 the other hand, becomes somewhat looser in texture and assumes 

 an asymmetrical quadripartite shape, in which form it enters the 

 equatorial plate to form the eccentric "accessory" chromosome. 

 The period at which the m-chromosomes condense varies consider- 

 ably, and the same is true of their relative position; sometimes they 

 are in contact, sometimes more or less widely separated, even lying 

 on opposite sides of the nucleus. Photo 21 shows two nuclei, 

 one above the other, in each of which appear both m-chromosomes, 



