Anatomical organization and molecular compositions of actin cap structures around the sperm head assembly inside head cyst cell. (A) Summary of the observations and indication of the positions of (a) the individualization stage, (b) coiled-up stage and (c) empty cysts inside a testis (gray out line). The positions of germ line stem cell (GSC) at the apex and the head and tail cyst cells are marked with distinct colors as indicated in the figure. The axoneme of maturing spermatids (black), the cell nuclei (blue) and major F-actin based structures (red) are highlighted to illustrate the basic observation of this study. The rostral ends of the sperm nuclei moved very slowly towards seminal vesicle during individualization until the mature sperm penetrate the head cyst cell to enter the seminal vesicle. (B) Cross-section view of the relative organizations of actin caps inside head cyst cell and sperm heads during individualization. It is partly adapted from a previous description  and updated to summarize the data presented in this report. Only four spermatids are drawn for simplicity in illustrating the organization. The compositions of the different regions are indicated by color coding as shown in the adjacent panel.