SPERMATOGENESIS OF THE PIG. 1 9 



as to render a count impossible (Fig. 54). Not infrequently the 

 chromosomes in the early spermatids become closely appressed 

 before they begin to break up (Figs. 53 and 57). Sometimes the 

 individuality of the chromosomes is apparent even after the 

 nuclear wall begins to form (Fig. 58). 



SPERMATIDS. 



From the foregoing evidence it is obvious that there exists 

 a dimorphism among the spermatids, one type containing eight 

 and the other ten chromosomes after the last division. The 

 chromosomes soon become irregular in shape and begin to break 

 up, and the spermatids appear all alike except that immediately 

 after the chromosomes disintegrate two nucleoli are visible in 

 approximately half of the cells (Figs. 64 and 65). These retain 

 for a short time the staining capacity characteristic of the 

 nucleoli of the previous stages, but later disappear and the whole 

 nucleus assumes a coarse granular appearance. The cells seem- 

 ingly remain quiescent in that condition for some time as they 

 are nearly always found in large numbers. The centrosome sur- 

 rounded by a clear layer is again very conspicuous within the 

 comparatively small centrosphere which lies close to the nucleus 

 (Figs. 64 and 65). 



DEVELOPMENT OF THE SPERMATOZOA. 



Following the period of rest the spermatids begin to develop 

 into spermatozoa. There is no perceptible change in the size 

 of any of the parts, such as described by Jordan in the opossum. 

 The first change to be detected is the extrusion of the centrosome, 

 surrounded by a light area, from the small sphere (Fig. 66). 

 It takes a position a short distance from the nucleus and soon 

 begins to divide. The two new centrosomes move apart and one, 

 somewhat rod-shaped, comes in contact with the nuclear wall but 

 it remains connected by a mass of material with the other centro- 

 some which assumes a disk shape and for a while remains in 

 place (Figs. 67, 68 and 69). The disk is frequently perforated in 

 the middle and has the appearance of a ring (Fig. 70). 



Simultaneously with the division of the centrosome, a portion 

 of the sphere which remains in close contact with the nuclear wall 



