579 



3) The odd chromosome not infrequently reveals a tripartite 

 structure. Less often one of its components seems to stand more or 

 less apart and behaves much after the manner of a "supernumerary" 

 chromosome. 



4) The odd chromosome passes undivided to one pole in the vast 

 majority of cases. Thus one daughter cell receives eight, the other 

 nine chromosomes. 



5) In the second division of the spermatocytes the eight chromo- 

 somes of the former division pair to form four chromosomes. Likewise 

 eight of the nine which passed to the other daughter cell pair to form 

 four but the odd remains unpaired. 



6) In this second division the odd chromosomes after lagging 

 somewhat divides and thus there are formed two spermatids each 

 containing five chromosomes. The spermatids formed from the divi- 

 sion of secondary spermatocytes which contained but four chromosomes 

 receive only four chromosomes each. Thus the final result of the two 

 divisions of the spermatocytes is the production of four spermatids, 

 two of which receive four, and two five chromosomes. 



7) As in the guinea two sizes of spermatozoa are produced. 



8) The transformation of the spermatid nucleus into the head of 

 the spermatozoon comes about through the gradual concentration of 

 the chromatin into an elongated curved mass at one side within the 

 nucleus and the ultimate elongation of this mass. 



Explanation of the Plates. 



All drawings were made with the aid of a camera lucida. As they appear here 

 their magnification is about 2100 diameters with the exception of Fig. 35 which is about 

 800 diameters. While the chromosomes are represented as accurately as possible, no 

 special attempt has been made to show the details of the achromatic structures beyond 

 general outlines and relations. 



Fig. 1. Late prophase of spermatogonia! division showing seventeen (or eighteen) 

 chromosomes. 



Fig. 2. Late prophase of spermatogonia! division showing three small chromo- 

 somes or a tripartite chromosome (accessory ?) to one side of the main mass of chromosomes. 



Figs. 3, 4. Spiremes of primary spermatocytes; the one without, the other with 

 chromatin nucleoli. The apparently undue size of these two nuclei is the result of 

 flattening through pressure in a smear preparation. 



Fig. 5. Late prophase of division in a primary spermatocyte. The odd chromo- 

 some is the elongated one at the top. From a smear preparation. 



Fig. 6. Metaphase of division in a primary spermatocyte viewed diagonally from 

 above. From a smear preparation. 



Fig. 7. Metaphase of division in a primary spermatocyte. The odd chromosome 

 which has advanced to one pole, shows a tripartite structure. From a smear preparation. 



Fig. 8. Primary spermatocyte showing the end of the odd chromosome projecting 

 beyond the general level of the equatorial plate. 



Fig. 9. Chomosomes of a primary spermatocyte. A tripartite odd or a curved 

 odd and a supernumerary (?) lie to the right. 



Fig. 10. Cliromosomes of a primary spermatocyte. A rare case in which one 



37* 



