MARSUPIAL SPERMATOGENESIS 215 



Tlie side-view of an early anaphase of the first meiotic division 

 is shown in fig. 25. The X- and the minute Y-chromosome are 

 on opposite sides of the central mass of chromosomes, and are 

 travelhng towards the poles of the cell ahead of the other 

 chromosomes. The first meiotic division therefore acts as 

 the reductional division and the two daughter secondary 

 spermatocytes produced are dimorphic, one containing the 

 X-chromosome and the other containing the Y-chromosome. 

 Satisfactory second meiotic division figures have up to the 

 present not been obtained. 



Spermatogenesis of Dasyurus maculatus. 



Only the male of this species was obtained, and so a check 

 count of the number of chromosomes of the female could not 

 be obtained. However, very good counts from spermatogonia! 

 metaphase plates were obtained leaving no doubt as to the 

 number of chromosomes present. The number of chromosomes 

 in this animal is the same as in Sarcophilus, a member 

 of the same family. Of the fourteen chromosomes, twelve are 

 the autosomes, one is the small X-chromosome, and the other 

 the minute Y-chromosome (PI. 16, figs. 26 and 27). 



From figures of the first meiotic division, the separation of the 

 X- and the Y-chromosome is seen to take place as in the other 

 animals (PI. 16, fig. 28). 



Summary. 



In the three animals studied the total number of chromo- 

 somes in the male is as follows : 



Phascolarctus 16 (14 autosomes +XY). 

 Sarcophilus 14 (12 autosomes -hXY). 

 Dasyurus 14 (12 autosomes + XY). 



In the female the number of chromosomes is as follows : 

 Phascolarctus 16 (14 autosomes -I- XX). 

 Sarcophilus 14 (12 autosomes + XX). 

 In all animals dealt with in this paper the Y-chromosome is 



very minute in size compared with the other chromosomes ; 



NO. 266 Q 



