THE SPERMATOGENESIS OF IXJilESTIC MAUJIALS. 



221 



Among the bivalent chromosomes n short, hirgo chromosome appears 

 which may bo the accessory one (Figs. 105, 106). At the end of tliis stage 

 tliis body cnn not bo made out, as every chromosome now becomes shortened 

 and the bivalent form almost disapi>ear3. 



In tliis stage it is not difficult to distinguish each chroinusomo aud so 

 to count tluur number, as the cliromosomes are distinctly separated (Figs. 

 104, 105). For coimting the du-omosomes, only those cells were selected in 

 which the chromosomes are well separated. It was found tliiit all such cells 

 always contain twenty four clu'omosomes. Thas it is certain thiit the reduced 

 number of cliromosomes in tlie male germ cells is twenty four, accordingly 

 the s^x^rmatogoniiü clmamosomes are probably forty seven in number, consisting 

 of forty six univalent clu'omosomes and an odd one. 



Tlie nucleolus usually disappears at the beginning of this st;ige, but 

 sometimes it still remains till the end of this stage. In every stiigo it can 

 clearly Ix; discerned by its distinctive staining capacity with Auerbach's 

 method (Figs. 149, 150). The beluivior of the mitochondi'ial gi-anules and 

 idiozome are entirely similar to that of the mouse. 



III. The Kedcction Diision. 



A. The reduction division in the mouse. 



The first reduction division: — In the pohxr view of tlie equatorial plate 

 of tbe metiiphase the chi'omosomes are distinctly separated aud so it is not 

 difficult to make out every chromosome and to count them exactly (Figs. 37- 

 41). In the early metaphase the cliaracteristic form of the (etrad still appeal's, 

 sliowing distinct sxnd constiint differences in size and form (Figs. 37, 38). In 

 most of the metaphase tlie number of the chromosomes is always coimted to 

 be twenty which represents lialf the number of the chi'omosomes of the 

 siDermatogonia (Figs. 37, 41). AVhen the cliromosomes are compared accord- 

 ing to their size it is foimd tliat, even though they form a series differing 

 very gradually from the largest to the smallest, they can be classiiied in three 

 groups ; nameh-, tlu-ee large sized, fifteen middle sized aud two small sized 

 ones (Figs. 38, 40, 41). If wo compue the sent« of the spermatogouial 

 chromosomes -with tLat of the luiploid ones, we can clearly recognize th-it the 



