120 J. F. MCCLENDON. 



Explanation of Plate I. 



All the figures were drawn with Abbe Camera, Zeiss apochromat objective 2 mm., 

 compensating ocular 12. They represent optical sections of varying thickness, of ele- 

 ments of the testes of Pandarus sinuatus Say. 



Fig. I. Spermatogonium. The black spheres are nucleoli. 



Fig. 2. Anaphase of the last spermatogonia! mitosis, seven of the divided chro- 

 mosomes are shown. 



Fig. 3. Telophase of the last spermatogonia! mitosis. 



Fig. 4. Resting stage of primary spermatocyte. The two black spheres are 

 nucleoli. 



Fig. 5- Presynapsis stage of the primary spermatocyte. The chromosomes are 

 in the form of threads and are sixteen in number, but not all are shown in the figure. 



Fig. 6. Commencement of synapsis. The chromosomes are denser than in the 

 preceding figure. 



Fig. 7. Synapsis stage. The chromosomes are so close together that they cannot 

 be counted. 



Fig. 8. Post-synapsis stage. The chromosomes have paired to form eight biva- 

 lent elements. 



Fig. 9. Prophase of first spermatocy tic mitosis. The chromosomes have shortened. 



Fig. 10. Later prophase. The bivalent chromosomes are transformed into tetrads 

 by a longitudinal furrow. 



Fig. 11. Late prophase. The tetrads have become still more shortened. 



Fig. 12. Metaphase of first spermatocy tic mitosis. 



Fig. 13. Equatorial plate of first spermatocytic mitosis. The eight tetrads are 

 shown. 



Fig. 14. Telophase of first spermatocytic mitosis. 



Fig. 15. Metaphase of second spermatocytic mitosis. 



Fig. 16. Telophase of second spermatocytic mitosis. 



Fig. 17. Late telophase of same. 



Fig. 18. Spermatid. 



Figs. 19-22. Stages in elongation of the spermatid to form the spermatozoon. 



In Fig. 21 some of the cytoplasm is being lost and the cell boundary is granular. 



In Fig. 22, which represents the spermatozoon, the elongated nucleus and its thin 

 covering of cytoplasm cannot be separately distinguished. 



Figs. 23-26 represent stages in the formation of a nutritive sphere from a sper- 

 matid. 



In Fig. 23 the cytoplasm has decreased in amount and the chromatin has collected 

 into lumps at the periphery of the nucleus. 



In Fig. 24 the cytoplasm has disappeared save for a thin granular layer, and the 

 nucleus is distended by the nutritive sphere. 



In Fig. 25 the nutritive sphere has increased in size and become denser, while the 

 cytoplasm has entirely disappeared. 



In Fig. 26 the nuclear wall has disappeared and the chromatin forms lumps on the 

 surface of the nutritive sphere. 



