MATURATION 141 



here, is along the line of a split which is usually visible in the 

 chromosomes when they appear out of the resting nucleus. 

 As the result of this heterotype division each secondary 

 spermatocyte receives the haploid number of chromosomes. 

 The second maturation division commonly shows none of these 

 rings or crosses, or other figures, and is known consequently 

 as the homotype division (Flemming's terms). The homotype 

 division of the secondary spermatocyte follows the heterotype 

 either immediately, or after a considerable pause, during which 

 the chromosomes sometimes lose their definite outlines to some 

 extent. This pause, which does not occur when tetrads are 

 formed, is probably related to the fact that while in the tetrads 

 both divisions of the chromosomes occur at the commencement 

 of the process, in this form of reducing division the second split- 

 ting does not occur until after its first actual division. During 

 the homotype division the chromosomes behave, then, essen- 

 tially as in the divisions of the usual type, and the resulting 

 spermatids receive, just as in tetrad formation, the haploid 

 number of chromosomes, just as do the secondary spermato- 

 cytes. Numerically, the most important difference in reduc- 

 tion with and without tetrad formation is that in tetrad forma- 

 tion the secondary spermatocytes have the diploid number, 

 and in the absence of tetrads, the haploid number of chromo- 

 jjomes*. This is the result of the fact that when tetrads are 

 formed, the division of the chromosomes actually belonging to 

 the secondary spermatocytes (second maturation division) 

 really occurs in the nucleus of the primary spermatocyte (first 

 maturation division), while in the absence of tetrads the divi- 

 sion of the chromosomes has the normal relation to cell division, 

 and the haploid number persists from the primary spermatocyte, 

 after synapsis, to the spermatid and spermatozoon. 



Before mentioning any further details of chromosome behav- 

 ior during maturation, we must compare the process of matura- 

 tion as it occurs in the ovum with that in the sperm. We may 

 say at the outset that in all essentials the two histories are 

 identical, so that this comparison may be brief, but there are a 

 few differences to be noted. 



