ABSTRACT
A cytological and quantitative study was made of the testes of foetal and neonatal rats. The population of germ cells was estimated for a total of 111 specimens. A volumetric method (Beaumont & Mandl, 1962) was used for animals aged 14.5 days p.c. to 4.5 days p.p. Counts were made of the numbers of dividing germ cells in foetal testes. Numbers of normal, degenerating and dividing gonocytes, ‘transitional’ cells and spermatogonia type-A were estimated from differential counts made on specimens aged 3-6.5 days p.p.
The primordial germ cells divide mitotically up to the age of about 18.5 days p.c. Thereafter they remain at interphase for a period of 6-8 days, during which they enlarge considerably. Although many gonocytes appear to undergo degeneration during this resting period, few ‘disappear’ from the testis until 2-4 days after birth. Differentiation of gonocytes into definitive germ cells sets in about 4 days p.p. The formation of spermatogonia type-A is preceded by the appearance of ‘transitional’ cells and a renewal of mitotic activity.
The total population of primordial germ cells rises from about 20,000 at 14..5 days p.c. to.reach a plateau of 120,000-140,000 between 20 days p.c. and 2 days p.p. The number of gonocytes then declines to ca. 50,000 at 6-6.5 days after birth. This decrease is due to (a) the elimination of degenerating germ cells, and (b) the transformation of gonocytes into definitive germ cells. With the re-initiation of mitotic activity, which accompanies germinal differentiation, the total population of germ cells increases to ca. 200,000 at 6-6.5 days, of which spermatogonia type-A number between 50,000 and 90,000.