MARSUPIAL SPERMATOGENESIS 217 



EXPLANATION OF PLATES 15 AND 16. 



Reference Letters, 



A, archoplasmic mass. E, excretory body. D, deutoplasm. P, plasmo- 

 some. Px, Plasmosome associated with X-chromosome. Px', plasmosome 

 derived from Px. Chr, chromatoid body. 



Plate 15. 



Phascolarctus cinereus. 



Fig. 1. — Female, Nucleus of a cell from the corpus luteum. The two 

 sex chromosomes (XX) are much smaller than any of the fourteen auto- 

 somes. (Bouin.) 



Fig, 2, — Sperraatogonial plate with fourteen autosomes surrounding 

 the X- and Y-chromosomes. (Bouin.) 



Fig, 3. — Spermatogonial plate. The constrictions seen at the end of 

 some of the chromosomes are not usually present. (Bouin.) 



Fig. 4. — Late leptonema, and beginning of synizesis. Only some of the 

 threads are shown, Chromomeres are distinct on some of the threads, 

 (Flemming.) 



Fig, 5, — Late synizesis and syndesis. Incomplete nucleus. Showing the 

 pairing of the chromomeres on homologous chromosomes. Central mass 

 representing the synizetic contraction. (Bouin.) 



Fig. 6. — Early pachjoiema. Thick-looped chromosomes still showing 

 some duplicity. (Flemming.) 



Fig. 7. — Showing the condensation of the sex chromosome, also the 

 associated plasmosome containing deeply staining granules. C, chromatic 

 granule in nucleus which probably gives rise to chromatoid body. (Bouin.) 



Figs, 8, 9. — Showing the presence of the second plasmosome {Px'). 

 (Bouin.) 



Fig. 10. — Early diplonema. Compact X-chromosome or XY bivalent. 

 Paired chromomeres distinct. 



Fig. IL — Later diplonema, (Bouin.) 



Fig, 12. — Metaphase plate of first meiotic division just after nuclear 

 membrane has disappeared. (Bouin.) 



Fig. 13. — Later metaphase plate. (Flemming.) 



Fig. 14, — Metaphase (side-view), X- and Y-chromosomes travelling to 

 opposite poles of the cell ahead of the other chromosomes, (Bouin,) 



Fig, 15, — Anaphase of first meiotic division, X and Y lagging behind 

 on the spindle. (Bouin.) 



Q 2 



