(1) In Smerinthus populi, Pieris brassicæ, and a number of other species of moths and butterflies the cytoplasmic bodies have been followed out.

(2) The micromitosome lias been followed from the spermatocyte back into the secondary spermatogonium. It is very probably present in the primordial germ-cell.

(3) The micromitosome has been definitely found in the female.

(4) The micromitosome seems to divide in all divisions, and I consider that it is a constant factor in the spermatids of Smerinthus.

(5) The probable nature and function of the micromitosome is discussed.

(6) The mitochondria have been carefully examined in the male and female germ-cell in all stages except in the maturation division of the female and in fertilisation.

(7) It has been shown that in early stages the cytoplasmic bodies of the female resemble those of the male.

(8) There is a definite period, judged to be about the beginning of growth stage, when the subsequent fate of the mitochondria in the male becomes different from that of the female.

(9) The remarkable formation of chromophobe and chromophile zones in the male mitochondrial body aud the use of these zones are described.

(10) The formation of the macromitosome from the mitochondria is described.

(11) The changes undergone by the macromitosome in sperm formation are followed out.

(12) The presence of the acroblasts in the fairly early growth period of the spermatocyte is described.

(13) The complicated evolutions of these bodies in division of the cells, their subsequent fate and' their probable nature are discussed.

(14) The staining and fixing reactions of the cytoplasmic bodies are fully described.

(15) A number of abnormalities have been described.

(16) The centrosome has been shown to divide in the young spermatid, and one centrosome is probably lost, but definite evidence is not forthcoming.

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