THE Sl'ERMATOOENESLS Ol' IXJMESTIC MAMMALS. 225 



aggregation of tho chromosomes iu tlio first divisiou is to bo rcgurdod as the 

 iiiittu'al stjito of tho chromosomes at this s'jigo and not duo to tho influeuco 

 of tho fixation may Ic ctrtickukxl from the fact that tho diploid chromosomes 

 occuriug iu the same tubule are tlistinctly separated from each other. In a 

 good polar view of tho equatorial plate of tho motaphaso the number of tho 

 chromosDxcs is rather difliciilt to determine but may bo couuttnl as over 

 twenty (Fig. 103). 



In the equatorial pLito of this division all tho chromosomes, ,excepl; the 

 accessory one, become so placed that the con-strictiou of every one of them 

 coincides with tho eqmxtorial plate (Figs. 107, 108). The division begins to 

 occiu" at this point of constriction where the spindle fiber atbiches and soon 

 the chromosomes become separated into their components (Fig. 109). 



If this plane of divisiou represents tho Uuo of tho coujngatiou of two 

 uuivalent chromosomes, then the conjugated uuivalont chromosomes mnsb be 

 separated and so tho fii-st divisiou is the reducing divisiou. When the 

 chromosomes thus separated move towtu'ds the res^xictivo poles, U- or V-slmj^)ed 

 oues can not be produced, they simply remain as short rod-shaped ones. 



In the metaphase when the onhuary chromosomes begin to divide, the 

 accessory passes undivided to one pole of tho spiudle in advance of the 

 ordinary chromosomes and can easily be distinguished fi'om the latter by its 

 s^xjcial form (Figs, 106, 107). Its behavior corresponds almost exactly with 

 that of the other mammals. Even though we cau not ti'ace this chromosome 

 as exactly as that iu the horse and cattle, we need not hesitate to identify it 

 with tho same. When all the chromosomes arrive at the poles they are 

 gatbered so closely together that their individual outliues can uot possibly bo 

 made out, the accessory at the same time disaj)pcariug from view (Fig. 

 110). 



The second reduction division : — As iu tho fii-st division, so in tho second 

 division the chromosomes have a tendency to gather into a mass so closely 

 together that it is chfficult to distinguish every chromosome and so to count 

 them (Fig. 112). In this divisiou all the chromosomes ai-e so an-anged that 

 their transverse constrictions •\\hich probably rei^reseut tho longitudinal 

 sjilitting, coincide with the equatorial phite, and thus they begiu to divide 

 into two jwrtions by tho separation of tho daughtor chromosomes at tho 



