EXPLANATION OF PLATES XVIII, XIX, XX. 



All drawiugs were made by the author with the aid of an Abbe camera lucida, and 

 are reproduced here at a magnification of about 1895 diameters. They are numliered 

 as nearly as possible in the order of their development. Figures 7, 8 and '.) are the 

 only exceptions. They represent the earliest cells that were studied, and have been 

 placed with the later spermatocyte stages merely for convenience. Figures 1-6 and 

 30-46 are from cells stained with iron-hsematoxylin and figures 7-29 from those 

 stained with Flemming's tricolor. 



Figs. 1-6. — Spermatogonia, polar views of the metaphase. Figures 1-4 

 are from a single individual and 5 and 6 from two others. There are 

 twenty-three chromosomes in each cell. The larger of them lie in the 

 outside portion of the plate and the smaller ones nearer the center. 

 The chromosomes are usually split (figs. 1, 2 and 6) and the halves 

 ready to go to the poles. The separation of the halves begins at the 

 inner end of the chromosome (fig. 6). 



Fig. 7. — Early secondary spermatogonium. X, Accessoiy chromosome in 

 its vesicle. N, Nucleoli, weakly stained but homogeneous. 



Fig. 8. — Spermatogonium, late telophase, within a cyst of about twenty 

 cells. X, Accessory, its vesicle well shown. A^, Nucleoli stained with 

 safranin. 



Fig. 9. — Another cell from the same cyst. Accessory seen in cross-sec- 

 tion within its vesicle; other chromosomes in cross-section also. 



Figs. 10-15. — Different stages from one follicle, not long after the last 

 spermatogonial division. 



Fig. 10. — Spermatogonium, telophase just after the last division. Cells 

 of this stage are deeply stained. The nucleus is at its smallest volume 

 here. The ordinary chromosomes begin to loosen up. The accessoiy 

 remains condensed. The occurrence of two nucleoli in each cell seems 

 to be quite general for the cyst. 



Fig. 11. — Telophase later than the above; in a neighboring cyst. The 

 chromatin is well diffused. A'', A^, Two faintly stained irregular nu- 

 cleolar bodies; nucleus still small. K, Karyosome, probably. 



Figs. 12, 13, 14, 15. — Spermatocytes, growth period. All from same 

 cyst. Accessory much condensed and massed into an irregular lump, 

 still clinging to the nuclear wall. Two nucleoli present in each cell, 

 stained with safranin like the accessory, sometimes differing slightly 

 in size. In figures 14 and 15 they lie in close contact, possibly uniting. 

 In the cells at the proximal end of this follicle there is but a single 

 nucleolar body besides the accessory present. This body is about equal 

 in volume to the two nucleoli, such as in figures 14 or 15. K, Mass 

 of chromatin, probably a tardy loosening up of a chromosome. 



Figs. 16-22. — Spermatocytes, growth period following the above. All 

 from one follicle. 



