Abstract
A study of spermatogenesis was made on four groups of a pedigreed strain of the moth Philosamia cynthia, and the results were compared with spermatogenesis in the wild material.
Deviations from the normal number of chromosomes were observed in two groups. In some individuals the haploid number was 12 instead of 13. Giant spermatocytes were also observed with twentyโfour chromosomes. In other individuals, two haploid numbers, 13 and 14, occurred in the same testis.
The twelveโchromosome condition is due to linkage of two chromosomes during the late prophase of the primary spermatocyte. The double chromosomes thus formed appeared to divide equally in both divisions. The origin of the fourteenth chromosome was not determined.
Correlation of the genetic and cytological data indicates the restriction of aberrant chromosome complexes to two of the four groups and the regularity of the twelveโchromosome complex in certain families, suggesting the conclusion that a new strain arose in the pedigreed material with regard to chromosome variability and that the twelveโchromosome condition is a wellโdefined characteristic, partly established in some families and probably fully established in others.