Pair of Heterochromosomes in Forficula 233 



ference between the two lots of material proved to be slight, if 

 indeed there be any difference. The small heterochromosome is 

 often flattened so that it looks smaller in side than in face view 

 (Figs._28 (H)_, 35 (H), 24 (E), 27 (E), 31 (E), 33 (E)). In either 

 material the inequality in size of the components of this pair is 

 conspicuous enough so that it is difficult to understand how any- 

 one who was looking for heterochromosomes could overlook it. 



As to the method of formation of tetrads I should disagree with 

 Zweiger and agree with Sinety in finding them formed in a manner 

 typical for many insects, by transverse division and longitudinal 

 splitting of the telosynaptic pairs of bivalents. 



The indications are either that Forficula auricularia must be 

 variable as to number of chromosomes in different localities, or 

 that it is a composite species made up of several small species dif- 

 fering in number and behavior of their chromosomes. According 

 to the latter supposition which seems to me the more probable, 

 Sinety's material with 24 and 12 chromosomes in spermatogonia 

 and spermatocytes respectively, is a different small species from 

 mine with usually 24 and 12 but sometimes 11 or 13 in the second 

 spermatocytes, and both are different from Zweiger's which has 

 24, 26 or 28 in spermatogonia and 12, 13 or 14 in the spermatocytes. 

 The peculiarity about Zweiger's numbers that I am unable to 

 understand, is his finding the number of chromosomes different in 

 first spermatocyte cysts of the same testis. I have always 

 found the number in the first spermatocytes of insects constant 

 for the individual. In cases like Diabrotica soror and D. 12- 

 punctata, I get variable numbers in the spermatogonia and 

 first spermatocytes of different individuals, but for each individual 

 the spermatogonial and first spermatocyte numbers are constant 

 while the second spermatocyte number is variable, as I find it in 

 Forficula. 



SUMMARY 



I In my material of Forficula auricularia, collected in Helgo- 

 land and Eisenach, Germany, I find 24 chromosomes in the sper- 

 matogonia, 12 in first spermatocytes, and usually 12 in second 



