The chromosomes in the parthenogenetic and sexual eggs of phylloxerans and aphids

Abstract

An examination of the ovarian parthenogenetic and sexual eggs of aphids and phylloxerans has shown that the synapsis stage is entirely omitted in the parthenogenetic eggs, both male- and female-producing; while on the other hand the sexual eggs pass through a synapsis period, i. e., a. period when the chromosomes contract to one side of the nucleus reappearing later in the reduced number. These observations show that the full number of chromosomes in these parthenogenetic eggs is due to the omission of a synapsis period, and not due to a separation of the chromosomes subsequent to synapsis. Synapsis appears, therefore, to be a phenomenon associated with the union of the paired chromosomes and to have no other significance for development.

Two years ago I reported that two classes of spermatozoa are formed in phylloxerans, as in other insects, but that the male-producing class degenerates. Consequently all the fertilized eggs have the female number of chromosomes. I reported that, nevertheless, when males appear in the later life cycle, they have a smaller number of chromosomes (one or two less) than the parthenogenetic female or the sexual female.