90 Don W. Fawcett and Mario H. Burgos 



Condensation of the karyoplasm 



After formation of the head cap a sequence of striking 

 changes is observed in the nucleus. Throughout the early 

 stages of differentiation, the karyoplasm of the spermatid 

 consists of closely-packed fine granules (circa 100 a) of rather 

 low density, interrupted here and there by coarser granules of 

 somewhat greater density (Figs. 4 and 5). The nucleolus is 

 inconspicuous and indefinite in outline. During the period of 

 elongation of the nucleus, the fine granules in the karyoplasm 

 are gradually replaced by coarser granules. These probably 

 arise by agglomeration of the pre-existing fine granules. 

 However, more seems to be involved than a change in the 

 state of aggregation of the nuclear material for, associated 

 with the increase in granule size, there is a marked increase in 

 their osmiophilia (Fig. 7). This must reflect an increase in the 

 number of unsaturated linkages. As differentiation continues 

 and the coarse granules become more closely packed, some 

 sperm heads show sizeable clear areas of irregular shape 

 which, no doubt, correspond to the " vacuoles " that have been 

 observed with the light microscope in the heads of human 

 spermatozoa. These have not been seen in the other species 

 studied. Late in the maturation of the spermatids, the coarse 

 dense granules (300-400 A) coalesce into a smooth homo- 

 geneous mass which once again displays only a moderate 

 affinity for osmium. Concurrently with these changes in the 

 fine structure of the karyoplasm there is a steady reduction 

 in the size of the nucleus and a change in the shape of its 

 sagittal section from obtuse to acuminate. 



The electron microscope finding, that there is a waxing and 

 waning of the osmiophilia of the nucleus, is reminiscent of the 

 earlier reports in the literature to the effect that there is a 

 progressive increase in nuclear staining with iron haematoxylin 

 during the intermediate stages of spermatid differentiation, 

 followed by a diminished uptake of the dye later on when the 

 spermatozoa are maturing. 



The increase in intensity of nuclear staining in the course of 



