Testicular development in Macaca irus after birth.

The seminiferous epithelium of 34 pre-pubertal, 1 pubertal and 6 adult Macaca irus (syn. Macaca fascicularis, cynomolgus monkey) was studied histologically. The testicular weight roughly doubled each year up to 3.5 years after birth, whereafter a 25-fold increase occurred with puberty. During the first year, the abundant interstitial connective tissue present at birth, was replaced by seminiferous cords that expanded by longitudinal growth. Few changes were seen within the tubules up to 3 years. Adark and Apale spermatogonia were already present in the stillborn monkeys. Before puberty much more Adark than Apale spermatogonia were counted, the Ad/Ap ratio varying between 1.5 and 6.9 before puberty and between 0.8 and 1.3 in the adult. B spermatogonia were present in small numbers after the first year. At puberty large numbers of spermatocytes and spermatids were found. Small testis fragments were incubated with [3H]thymidine and processed for autoradiography. Very few labelled Adark spermatogonia were found both before and after puberty. The Labelling Index (L.I.) for Apale spermatogonia was constant before puberty (6.5%), but increased to 14.9% thereafter. The L.I. for B spermatogonia was 18.7% in the adult. Before puberty the L.I. of Sertoli cells was low (0.27%) but constant. No labelled Sertoli cells were observed in adult monkeys. It is discussed that proliferating adult type A spermatogonia are present between birth and puberty but that, in contrast to the adult situation, differentiation of these cells into B spermatogonia is limited.