CH. I] FORMATION OF THE SEX-CELLS 9 



the threads. According to Boveri, the meaning of the forma- 

 tion of the tetrad is only the precocious separation of the chro- 

 matin-threads for two rapidly succeeding divisions (without an 

 intermediate resting- stage). The doubling of the chromosomes 

 previous to division has, he thinks, no further significance than 

 the preparation for two quickly succeeding divisions. It is not 

 obvious, however, in the development of the spermatozoon why 

 this rapid division should take place at this time and at no 

 other in the life of the cell. 



Meves ('96) has most recently reexamined the development 

 of the spermatozoon in the salamander. His results differ in 

 several respects from the earlier results of Flemming, and in 

 one essential respect from the work of vom Rath. According 

 to Meves, the germ-cells undergo many divisions in the upper 

 part of the testis. The chromatic figure is that of the usual 

 type of division ; and twenty-four chromosomes are present. As 

 a result of the division, the cells become smaller, and each cell 

 becomes surrounded by a layer of connective tissue. Each of 

 these cells then divides many times according to the usual type 

 of division, so that clusters of cells are produced surrounded by 

 a common wall of connective tissue. Then follows the resting- 

 period, in which the cells enlarge. After this the maturation- 

 divisions take place. Meves thinks that most probably each 

 cell divides only twice during this period, as in other forms. 

 The first division is heterotypic, and now for the first time the 

 number of chromosomes is reduced to twelve. Without a resting- 

 period each cell again divides, the twelve chromosomes splitting 

 longitudinally. This second division is homoeotypic. Each 

 cell, containing twelve chromosomes, then transforms directly 

 into a spermatozoon. 



Meves shows therefore that Flemming was mistaken in regard 

 to the number of cell-generations that are present in the sper- 

 matogenesis of the salamander, and further that Flemming 

 failed to make out the real sequence of the generations and 

 the number of chromosomes present in each. More important 

 is Meves' statement that, normally, there is not a formation of 

 tetrads as vom Rath had affirmed. At present it is impossible 

 to decide between the divergent accounts of Meves and vom 



