MALE REPRODUCTIVE CELLS 



447 



deeply stained (many in typical tetrad form), among which the acces- 

 sory is only occasionally recognizable where it has a large U-shaped 



FIG. 410. Aplopus Mayeri. 16, 17, and 18, three early prophases of the first reduction divi- 

 sion, all chromosomes except the accessory are still light staining; 19, prophase in which 

 the chromosomes are forming tetrads and the accessory is not recognizable because all the 

 chromosomes stain dark; 20, equatorial plates of four primary spermatocytes about to per- 

 form first reduction division. Each shows 18 chromosomes, one of which is the accessory. 

 X 1400. (Drawn by H. E. JORDAN.) 



form. Figure 20 shows equatorial plates of four contiguous primary 

 spermatocyte cells during the metaphase of the first maturation mitosis. 

 Each of the cells has 18 chromosomes, one of which is the acces- 



FlG. 411. Aplopus Mayeri. Four stages in the first reduction division, showing how, in the 

 operation, the accessory chromosome passes undivided to one of the daughter cells or sperm. 

 ac., accessory chromosome. X 1400. (Drawn by H. E. JORDAN.) 



sory, not recognizable, however, among the ordinary chromosomes. 

 It is one of the large eccentric bodies; other plates show the unmis- 



