SPERMATOGENESIS OF THE PIG. 



60; 



sol 



40 



30 



20 

 10 



m.m.-~ 10.5 11 US 12 12.5 13 135 14 14.5 15 15.5 16 



FIG. i. Diagram showing the variation in size among four hundred mature 

 pig spermatozoa. Figures at the left give the numbers of the individuals belong- 

 ing to each type. Figures at the bottom give the lengths of the heads of the 

 spermatozoa in millimeters, magnified two thousand times. 



VARIATION IN SIZE OF MATURE SPERMATOZOA. 

 The spermatozoa of the pig vary considerably in size, and 

 careful measurements revealed the fact that they may be arranged 

 in two separate classes, one type being much larger than the 

 other. Mature specimens, which were free in the lumen of the 

 tubule and parallel to the objective, were selected at random, and 

 outline sketches of four hundred heads enlarged (X 2,000) were 

 made with the aid of a camera-lucida. The lengths of the 

 sketches were then carefully measured and recorded in half 

 millimeters. Figure I in the text shows the variation in size 

 of the four hundred heads measured. It can be seen at a glance 

 that two separate types of spermatozoa exist ; the greatest num- 

 ber of the one kind measuring from 11.5 to 12 mm., and of the 

 other type from 14 to 14.5 mm. The increased size of the 

 latter is due presumably to the presence of the accessory chromo- 

 somes. 



RELATION OF THE ACCESSORY CHROMOSOMES TO SEX 



IN THE PIG. 



Many investigators working on the problem of sex determina- 

 tion are of the opinion that the sex of a zygote is determined at 

 the time of fertilization, the spermatozoan in most cases carrying 



