The transformation of male sex cells ofTetranychus urticaeK. (Acari, Tetranychidae) during passage from the testis to the oocytes: an electron microscopic study

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Abstract
The fine structure of the spermatozoon of Tetranychus urticae is described during passage from the testis to the site of insemination in the ovary. The male sex cells differentiate from a cytoplasmic mass which is characterised by nuclei bearing tubule-like structures. Infoldings appear in peripheral membrane of the germ cells at the beginning of spermiogenesis, chromatin condenses, and the nuclear membrane is reduced. The spermatozoon is surrounded by a double membrane: the inner one is the sperm membrane and the outer one is of somatic origin. The sperm reach the glanular region of the testis where they are transformed into amoeboid cell and are next collected in the seminal vesicle. After copulation, the sperm can be observed in the lumen of the receptaculum seminis of the female from which they soon enter the epithelial cells. Still surrounded by a double membrane, the sperm, which are now packed in clusters, develop microtubules immediately beneath the inner membrane and enlarge by decondensation of chromatin and by infiltration of cytoplasmic material. Insemination takes place in the vitellogenic region of the ovary just before the eggs close their pores; the sperm have now reached ten times their original size.