PLATE XVII. 



These plates were made with a Zeiss 2 mm. apochromatic objective, arc light 

 illumination, at an original magnification of 1000 diameters. In reproduction, 

 this has been reduced to 750 diameters, and so corresponds to that of the draw- 



Fig. A. — This represents the metaphase and anaphase of spermatogonia! di- 

 visions. So rapid are these cycles in their succession that the continuity of the 

 archoplasmic substance between the centers of the previous generation is not 

 lost. This simulates the "antipodal cone" of Boveri very closely. 



Fig. B. — The cells on the left of the spermatocyst wall are in the telophase 

 of the last spermatogonia! division. Cf. fig. 3. To the right of the wall are very 

 early prophases of the spermatocytes. Somewhat earlier than fig. 4. 



Fig. C. — Later first spermatocyte prophase, showing the character of the 

 chromatin segments and the linin connecting threads. Near the upper edge of 

 the figure is seen the accessory chromosome, marked by the smoothness of its 

 outline and the homogeneous, transparent structure. 



Fig. D. — In this figure is shown a chromatin segment with the central cleft 

 indicated in figs. 14, 15, 15a, and 17. 



Fig. E. — A segment as in D, accompanied by a ring showing the same 

 structure. Note the archoplasmic radiations proceeding from a center located 

 on the nuclear membrane, as shown in fig. 15a. 



Fig. F. — In the vipper part of the figure is exhibited a first spermatocyte in 

 the metaphase condition as viewed from the side. Chromosomes are seen in 

 difl'erent stages of division. The cell below presents the form of the elements in 

 the same stage when observed from the pole. 



Fig. G. — Two spermatocytes in the metaphase of division. Chromosomes in 

 various stages of separation shown. A central opening visible in the element at 

 the left of the figure. 



Fig. H. — Here are shown chromosomes in the form of loops and rings, with 

 the chromatin drawn out into a long thread by the contracting fibers attached to 

 them. Cf. figs. 22/t and 22/. 



Fig. I. — Another first spermatocyte metaphase in which are chromosomes at 

 about the middle stage of their separation. Cf. figs. 20, 226, and 22c. 



Fig. J. — Second spermatocyte metaphases. The radially disposed diads 

 with the chromatids superimposed in the plane of the spindle shown. Cf. figs-. 

 24 and 25. 



Fig. K. — An anaphase of the first spermatocyte, showing the diads near one 

 pole of the spindle. At the left a polar view of a trifle later stage. 



Fig. L. — Telophase of the first spermatocyte, in which are seen the ragged out- 

 line of the chromosomes and the persistent spindle fibers between the daughter 

 cells. Somewhat earlier than fig. 23. 



(Drawings and photomicrographs by the author.) 



