564 FERNANDUS PAYNE 



one case and have fused in the other. A few cells show 14 

 chromosomes. Side views of such cells show that ten of these 

 are bivalent and four univalent. In this case the components 

 of two bivalents have remained separate and the group as a whole 

 is the same as the one where 12 and 13 chromosomes appear in 

 polar views. 



The interesting thing about these univalent chromosomes is 

 not the fact that they are univalent, but their irregular behavior 

 in the two divisions which follow. So far as I know, with the 

 exception of the supernumerary chromosomes of Metapodius 

 and Diabrotica, the behavior of any univalent chromosome in 

 the two maturation divisions is regular, and such chromosomes 

 divide in one or the other division. The rule is for bivalent chro- 

 mosomes to divide twice and univalent chromosomes once. We 

 would expect then these univalent chromosomes in Forficula 

 to divide in one maturation division and not in the other. In 

 the first maturation division I find that they may or may not 

 divide and, whatever happens to them, they always lag behind 

 the others. Figure 2, S shows both of them divided; R shows 

 one divided, the other undivided. In Q it seems that both are 

 passing undivided to one pole. In P both are elongated and it 

 is impossible to say just what disposition will be made of them. 

 Sometimes they become more drawn out, and in such cases as 

 figure 4, A^ (a different individual), it seems very doubtful whether 

 one lagging chromosome will ever reach either pole. These 

 lagging chromosomes are the ones which Zweiger calls 'accesso- 

 rische Chromosomen.' I have seen only one anaphase with four 

 lagging chromosomes and it was not suitable for drawing. Hence 

 I have not been able to make out the distribution of the univalents 

 in the 14 chromosome groups. From this irregularity in the 

 behavior of these single chromosomes, it will be seen that the 

 number of chromosomes in the second maturation division will 

 vary. This is the case, and by actual count of polar views, 

 clear metaphase plates, I have found nine cells with 11 chromo- 

 somes; 65 with 12; 23 with 13 and four with 14. For these vari- 

 ations see figure 3, B, C, 14 chromosomes; D, E, F, 13 chromo- 

 somes; G, H, 12 chromosomes and /, J, K, 11 chromosomes. 



