Oogenesis in lorises; Loris tardigradus lydekkerianus and Nycticebus coucang

Abstract

A histological study of ovaries in three pairs of foetal and 67 pairs of postnatal slender lorises of different age groups ranging from suckling young to adults was made. Oogonia in interphase and mitosis, as well as non-follicular germ cells in various stages of meiotic prophase, were present in all the ovaries. Similar germ cells were also found in 12 pairs of postnatal slow loris ovaries. A quantitative estimation of the primordial germ cell population was also made in the 67 pairs of postnatal slender loris ovaries. The total number of germ cells decreases with age from the time of birth until puberty. In the adults the primordial germ cell population varies in relation to the different phases of the reproductive cycle. This suggests that oogenesis in postnatal lorises may be under endocrine control. The number of germ cells increases progressively during pro-oestrus and oestrus and reaches a peak of ca. 171000 cells during early pregnancy. Thereafter the number declines to a level of about 20000 during lactation and drops to a level of ca. 10000 during anoestrus. The fate of all the freshly formed germ cells during each oestrous cycle is not known. It is likely that most of them perish since the number of atretic cells is also high during phases of increased oogenetic activity. It remains to be shown whether any of the newly formed cells contribute to the definitive germ cell population.