368 ARTHUR C. WALTON. 



Fig. 4), indicating that the chromosomes of the first maturation 

 spindle are really di-tetrads, or octads, due to the presence of a 

 "Querkerbe" in each of the four components. The number of 

 chromosomes is easily seen to be eighteen (Plate I., Fig. 3). 



The anaphase of the first spermatocyte division shows that 

 the group of six small chromosomes lags behind (Plate I., Figs. 

 5-7), and goes undivided to one pole, thus constituting a hetero- 

 chromosome group of the X-type, and in the late anaphase this 

 group goes to one of the daughter plates (Fig. 7) ; thus forming 

 two types of spermatocytes, one having eighteen and the other 

 only twelve chromosomes. Polar views of the telophases of this 

 division show that one plate receives half of the autosome 

 material and all of the idiosome material, and that the other 

 daughter plate receives only one half of the autosome material 

 (Plate I., Figs. 8a and 86). Sister second spermatocytes in the 

 metaphase show very clearly the difference in the number of 

 chromosomes found in the two types of second spermatocytes 

 (Plate I., Fig. 9). Lateral views of the same stage show the size 

 difference in the equatorial plate (Plate I., Fig. ioa with 18 

 chromosomes, Fig. io& with 12 chromosomes). 



The second division of the spermatocytes is entirely regular, 

 each spermatid receiving one half the amount of chromatic 

 material. In lateral views of the telophase of the second divi- 

 sion the daughter plates from an eighteen chromosome second 

 spermatocyte are larger than those from a twelve chromosome 

 second spermatocyte (Plate I., Figs, ua and lib). Two types 

 of spermatids can be recognized, those with larger nuclei and 

 those with smaller nuclei. The chromosomes at this stage have 

 become so diffused that they can no longer be distinguished as 

 individual bodies (Plate I., Fig. I2a, eighteen chromosomes; 

 Fig. I2&, twelve chromosomes). 



j 2. A. felis. 



Polar views of the metaphase plates of the first spermatocyte 

 division show nine tetrad chromosomes, one of which is asym- 

 metrical and larger than any of the remaining eight. This 

 large tetrad is composed of two unequal parts, the larger com- 

 ponent being as large as one of the ordinary tetrads. The smaller 



