ABSTRACT
The anterior region of the nucleus lacks chromatin, consisting solely of the nuclear membrane and that of the endonuclear canal. Further posteriorly it acquires chromatin which basally reaches a diameter of 1 pm. In the postacrosomal region the chromatin is rosette-shaped in transverse section owing to the presence of helical cortical bands. The nucleus has a deep basal implantation fossa which is almost entirely filled by the anterior end of the axial fiber. The two centrioles are situated very close together and lateral to the axial fiber. They and the anterior end of the axial fiber are surrounded by a dense fibrous bed or ring (identified with an annulus) which is connected to the nuclear membrane of the fossa by fine fibers. Sandoz (1974) states that the neck is composed of an ovoid mass, continuous with the axial fiber, inserted into the base of the nucleus. Sandoz (1974, 1975) equates it with the neck of urodeles and suggests that if may be compared to the centriolar annexe of insect sperm, the connecting piece of mammalian sperm, or ciliary rootlets of epithelia.
