46 



BXPLAUATION OP THK i<'IGURES. 



Fig. 1. Transverse section of a testicular tubule of a 

 small crat. Fixed In Petrunkewitsch* s fluid. Z600 Spermatogonia 

 at the top* Sperms at the "bottom, spermatids between. 



Fig. 2. Transverse section of testicular tubule, p.s., 

 primary spermatogonlal cell. The mass of spermatogonia larger 

 than in Pig. 1. 



Fig. 3. Transverse section of testicular tubule showing 

 larger mass of spermatogonia, p.s., primary spermatogonlal 

 cell. 



Fig. 4. Transverse section of testicular tubule showing 

 a large mass of spermatocytes in synapsis, p.s., primary 

 spermatogonlal cell. 



Figures 5-llS (except 7u-72) were all drawn with the 

 camera lucida and a Zeiss 1.5 m.m. apochromatic objective and 

 a compensating ocular (either a No. 6 or XJo. 8). Then the 

 drawings were enlarged so that in the plates there is a mag- 

 nification of 3000 diameters. In making Pigs. 7u-72 the 

 camera lucida was not used. 



Fig. 5. Resting phase of a spermatogonlal nucleus. 



Fig. 6« Prophase of a spermatogonlal nucleus showing 

 the paired chromosomes which were seen in the upper one-half 

 of the nucleus. 



F ig. 7. Optical section df a spermatogonlal nucleus 

 showing the peripheral arrangement of the paired chromosomes 

 in the prophase. 



Fig. 8» The mitotic figure in a spermatogonlal division. 



Fig. 9. Early prophase of the first miotic division of 

 the spermatocyte . 



Fig. 10. SytapslB in the first miotic division of a 

 spermatocyte. 



JTlgs. 11 and 12. The stage following synapsis showing 

 the spireme loosened up and separating into chromosomes. 



Fig. 13. First miotic division, stage Jxlst preceding 

 the formation of the equatorial plate. 



Fig. 14. Equatorial plate and spindle in first miotic 

 division. 



Fig. 15 . A tripolar division of the nucleus of a sperma- 



