606 NATHAN FASTEN 



occur in this tissue would be to cultivate it in culture medium 

 and to observe the living cells multiply. 



Diu*ing the prophase of the earliest spermatogonia! stage 

 (fig, 1), the nucleus is large, round, and contains two or three 

 huge spherical karyosomes. Thin linin strands, granular in 

 appearance, radiate from these karyosomes to the periphery 

 of the nuclear wall. The cytoplasm has a granular appearance, 

 interspersed with slender fibrillae. Distributed through the 

 cytoplasm are larger, heavier-staining granules (figs. 1-2, M), 

 which in many cases become grouped mainly at one pole. These 

 appear to be mitochondrial granules, for with basic dyes they 

 stain almost as heavily as chromatin. Especially good prepar- 

 ations of these structures were obtained through the Meves- 

 Duesberg method. Large chromatoid masses (figs. 1-2, k) 

 are also found. The centrosome (figs. 1-2, C) can often be seen 

 lying in an open space surrounded by a denser cytoplasmic mass, 

 the idiozome (fig. 2, 7). Each spermatogonial cell is enclosed 

 by a definite cytoplasmic wall which marks it off distinctly from 

 its neighbors. 



As development proceeds, dense masses of chromatin make 

 their appearance in the nucleus along the radiating linin strands, 

 while the karyosomes begin to disappear. It appears as if this 

 increase in chromatin is the result of the fragmentation of the 

 karyosomes and the distribution of the chromatin along the 

 fibrous linin strands which radiate toward the nuclear periphery. 

 The cell in general, and especially the nucleus, stains more heavily 

 with the basic dyes. 



The masses of chromatin continue to increase within the 

 nucleus, forming a great many irregular clumps joined by thin 

 linin material. In the last spermatogonial prophases the nucleus 

 has somewhat increased in size and the irregular chromatin 

 masses have become distinct, the linin threads which united them 

 not being apparent any more (fig. 2). These masses vary in 

 numbers, as shown by the following counts in different cells: 

 86, 79, 74, 85. The centrosomes, which in the meantime have 

 divided, now begin to migrate to opposite poles of the cell and 

 the spindle fibers make their appearance. Binford ('13), has 



