172 EZRA ALLEN 



a function) until it lies against the nuclear membrane at the time 

 when the centrioles have placed themselves at the same point, 

 after which it breaks up into three small bodies which gradually 

 disappear in the cytoplasm after moving away from the nucleus. 

 As I have not studied spermiogenesis, I am in no position to 

 criticise these manifestly opposite results of Lenhossek and 

 Duesberg. 



5. CONCLUSIONS 



1. The diploid number of chromosomes in the male albino 

 rat (Mus norwegicus, var. alb.) is 37; the haploid number is 19. 



2. Sperm dimorphism is produced by the presence of one un- 

 paired accessory. It divides in the second maturation division. 



3. The constitution of the first spermatocyte chromosomes is 

 typically tetrad, with the four parts so organized that each may 

 retain its individuality. 



4. The shapes of the chromosomes in the spermatogonia are 

 all curved rods ; in the first spermatocytes, simple and compound 

 rings, crosses, and one rod, the accessory; in the second sperma- 

 tocytes, curved rods. 



5. Fiber attachment is terminal in the univalent chromosomes 

 throughout, and is fixed. 



. 6. No synizesis has been observed. 



7. Only one type of spermatogonia is present. These develop 

 from apparently indifferent cells which produce the Sertoli cells 

 also. I 



8. The first spermatocyte cells begin to differentiate between 

 the seventh and tenth days after birth. 



9. The first spermatozoa are ripe between the thirty-sixth and 

 fortieth days after birth, about the time of the descent of the 

 testes. 



10. A nucleolus (or plasmosome) is present in the first sperma- 

 tocytes. It seems to disintegrate and does not reappear in the 

 second spermatocytes. 



11. The specialized cytoplasmic structures are the idiosome 

 and the chromatoid bodv. 



