SPERMATOGENESIS OF THE HORSE. 305 



IX. VARIATION IN SIZE OF ADULT SPERMATOZOA. 



The spermatozoa of the horse like those of the pig vary con- 

 siderably in size and many careful measurements show that they, 

 too, are of two distinct types, the one 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 six hundred heads enlarged (X 2,000) 

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

 sketches were then measured and recorded in quarter millimeters. 

 It can be seen from Fig. I in the text that two separate types of 



7o 

 fco 

 So 



Vo 

 do 

 AO 

 10 



(07 if II * //*' n.1 1^. /a.y 



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

 horse spermatozoa. Figures at the left give the numbers of individuals belonging 

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

 tozoa in millimeters, magnified two thousand times. 



spermatozoa exist ; the greatest number of the one kind measur- 

 ing 9.5 mm., and of the other n mm. I think it is safe to 

 assume that this dimorphic condition in the size of the mature 

 spermatozoa is due to the accessory chromosome. The increased 

 size in the one type is due presumably to the presence of that 

 element. 



A similar dimorphic condition was found to exist among the 

 spermatozoa of the pig; one type measuring from n to 12 mm., 

 and the other from 14 to 14.5 mm. (Wodsedalek, '13). Size 

 dimorphism also exists in the adult spermatozoa of Anasa tristis 

 (Faust, '13). This of course is exactly what would be expected 



