16 J. E. WODSEDALEK. 



shows the two resulting cells of a primary spermatocyte division 

 which are still in close contact and both ready for dividing into 

 spermatids. Resting stages, however, appear in abundance and 

 in this stage, as was the case in the resting stage of the primary 

 spermatocyte, the centrosome surrounded by a clear zone becomes 

 large and very conspicuous (Figs. 41 and 42). 



2. Second Reduction Division (Equation al] . 



Although the division of the primary spermatocyte gave rise 

 to cells containing eight and ten chromosomes respectively (Figs 

 38, 39, 40), when these cells become ready for division half of 

 them show four (Figs. 13, 14, 43, 45, 46) and the other half six 

 chromosomes (Figs. 43, 44, 47). Thus a second pairing of the 

 ordinary chromosomes, similar to that found by Guyer in the 

 pigeon ('oo), corroborated by Geoffrey Smith ('12), man ('10), 

 guinea ('090.), and chicken ('096), and by Jordan in opossum 

 ('11), has evidently taken place so that there are four bivalents 

 in each type of cell and the additional two accessory chromosomes 

 in the one type. Stevens ('n) says that there is no such second 

 synapsis or numerical reduction in the guinea-pig. Figures 45 

 and 46 show four large chromosomes in the metaphase stage of 

 one type of secondary spermatocyte and Figs. 44 and 47 represent 

 the other type in which six chromosomes appear, four bivalent 

 autosomes plus the two accessories. The four chromosome 

 group is evidently formed by the pairing of the eight chromo- 

 somes of one type of cell resulting from the first maturation divi- 

 sion at one pole, and six chromosome group is interpreted as 

 being derived by the pairing of the eight chromosomes plus the 

 two unpaired accessories at the opposite pole (Figs. 38, 39, 40). 



Guyer ('10) in speaking of the second conjugation of the chro- 

 mosomes in man says : 



"Assuming that the respective chromosomes are more or less 

 qualitatively differentiated, such a numerical reduction, however, 

 by no means necessarily implies that there has also been a second 

 qualitative reduction. Aside from the improbability of such a 

 reduction, the general appearance of the divided chromosomes 

 would not warrant this interpretation; for instead of the elon- 

 gated univalent type as seen in the spermatogonia, or in ana- 



