The development and morphology of the gonads of the mouse. —IV. The post-natal growth of the testis

Abstract

Approx. 140 [male] mice, from an in-bred colony, ages ranging from birth to upwards of 300 days, were employed in this research. The cleaned-body weight and the weight of the testes was obtained for each animal. The data for the growth to age relations of (a) cleaned-body weight, (b) weight of testes, (c) mean diameter of spermatic tubules, (d) - area of spermatic tubules in transverse section, (e) area of intertubular tissue in transverse section, together with the growth of testes to cleaned-body weight, are given in the form of scatter diagrams. A linear regression has been fitted for the right testis on the left and it is shown that the right testis is significantly heavier than the left. The max. number of primary spermatocyte nuclei in pachynema occurs on the 14th day, together with the appearance of a lumen in many of the spermatic cords, while at about the same time the increase in the mean diam. of the spermatic tubules attains a max. and all the cords become ruminate. Mature sperms appear first in the testis of the mouse on the 42nd day; in the rat on the 37th. (Allen, 1918.) The appearance of mature sperms in the testis provides an easily determined and clearly defined point in the period of puberty. From birth to puberty, so denned, the rat increases its body weight by 8 times, the mouse by 9 times. Afterwards whereas the rat attains a weight 8 times that at puberty when it is a year old, the mouse only doubles its weight from puberty to about 300 days. The testes attain their maximum growth rate at 30 to 40 days, at the time when the area of spermatic tubules in a transverse section relative to the area of intertubular tissue is at a maximum. Although there is a greater tendency towards degeneration of a small percentage of germ-cells in some of the spermatic tubules about the time when the majority of spermatocytes are in pachynema, no generalized wave of degeneration, such as has been described in some mammals, occurs between birth and maturity.