354 EDMUND B. WILSON 



3. The interkinesis 



The interkinesis has hitherto been very briefly treated by my- 

 self and other observers of the insects, because in most species the 

 chromosomes are so closely crowded at this time as to preclude 

 accurate study. Lygaeus (at least in my material) is no excep- 

 tion to this, but Oncopeltus fortunately shows every stage of the 

 interkinesis with remarkable, clearness. There is no 'resting 

 stage' between the two divisions, no nuclear vacuole is formed, 

 and both the chromosomes and the centrioles retain their individ- 

 uality throughout. 



At the moment when the equatorial furrow has appeared and 

 the conjugation of X and Y has taken place, the centrioles are 

 already rather far apart, and still lie at some distance from the 

 chromosome-group (fig. 22) . All the achromatic elements are now 

 so delicate that it is difficult to make sure of the exact structure; 

 but it is certain that each centriole is surrounded by a small, but 

 very distinct aster, and the two seem to be connected by a delicate 

 central spindle. As the cell divides several other changes take 

 place. The chromosomes, without otherwise changing their 

 grouping become still more crowded together, and thus become 

 massed in a nearly flat plate, while the centrioles move still far- 

 ther apart (fig. 23). Shortly after the division these relations 

 are unchanged save that the centrioles are still farther separated 

 and lie nearly on opposite sides of the chromosome-group. The 

 asters are still present, and between them lies a rather large, 

 irregularly spindle-shaped area. It is difficult to say whether 

 this should be regarded as an actual spindle; but delicate fibrillae 

 often may be seen extending into it from the poles. 



The chromosome-group lies somewhat excentrically within this 

 area in the form of an irregular flattened plate. In side-view 

 (fig. 30) it is usually impossible to distinguish more than a few of 

 the chromosomes. In face view also, the crowding is often so 

 great that the grouping can not be exactly made out. Here and 

 there, however, it is evident that the original grouping has not 

 been lost, and occasionally plates are to be found in which every 

 chromosome may be clearly seen (figs. 31, 32). Study of such 



