1. Diploidy is the prevailing chromosomal complement in parthenogenetically developing turkey germ discs and embryos.2. The modal chromosomal count in normal turkey embryonic material is 72. On the basis of their size the chromosomes can be classified into macro-chromosomes and micro-chromosomes. The former can be further subdivided into two subgroups: (a) the largest eight are very conspicuous both in shape and size (because of this they have been used as markers in this study for ascertaining ploidy in the parthenogenetic material); (b) about ten middle-sized chromosomes.There are approximately 54 micro-chromosomes, with the number varying among the individual embryonic specimens, and within cells of the same specimen.3. The available parthenogenetic material has demonstrated the presence of two small, V-shaped chromosomes in the metaphase nuclear plates. These chromosomes were classed as sex chromosomes because of sex dimorphism in their number. On the basis of this, the genetic sex of the membranous growths and of embryos was determined to be male.4. In addition to normal diploid cells, the parthenogenetic specimens showed numerous polyploid (mostly tetraploid) plates. These were interpreted to be the product of the restitution nuclei fused into one, or of mitotic divisions in the binucleated cells.5. Small nuclear plates, interpreted to possess the haploid chromosomal complement, also occurred frequently in the parthenogenetic material. The occurrence of such plates may be a major factor responsible (either per se or due to recessive lethals) for the abortive nature of most of the instances of parthenogenetic development in turkeys.