306 J. E. WODSEDALEK. 



since the spermatogenesis studies of this form indicate that one 

 half of the spermatozoa receive one more chromosome each than 

 the other half (Paulmier, '99). 



X. MIGRATION OF THE DEVELOPING SPERMATOZOA. 

 In the very beginning of the transformation of the spermatids 

 into spermatozoa when the acrosome takes a position on the 

 nucleus opposite the dividing centrosome (Fig. 68), the anterior 

 end of the sperm-cell which bears the acrosome, invariably 

 points in the direction of the tubule wall and the Sertoli or nurse 

 cells. Long before the tail is sufficiently developed to aid in 

 locomotion these sperm-cells move a short distance and come in 

 contact in bunches with the nurse cells. There apparently 

 exists some attraction between the nurse cells and the nuclei of 

 the sperm cells in that stage of development. In this first stage 

 of migration only the nucleus appears to be attracted while the 

 cytoplasm exhibits a tendency to remain in place. The fact that 

 the cytoplasm does have a tendency to remain in place while 

 the nucleus or sperm-head moves forward undoubtedly accounts 

 for the posterior position that the entire mass of cytoplasm 

 assumes with respect to the sperm-head (Figs. 69-79). This 

 change in position of the cytoplasm to the posterior end of the 

 developing cell occurs simultaneously with the migration of the 

 cell, which is further evidence for such an assumption. The 

 nucleus is apparently attracted with sufficient intensity to 

 enable it to pull the entire cytoplasmic contents after it to a cer- 

 tain extent. In the later stages the movement of the sperm-head 

 deeper into the cytoplasm of the nurse-cell is probably facilitated 

 by the flagellum-like motion of the filament which extends a 

 considerable distance out of the cell (Figs. 75-79). Later, when 

 the spermatozoa are almost fully developed and slough off the 

 balls of naked cytoplasm (Figs. 85 and 86) they back out aAvay 

 from the nurse-cells, becoming embedded in the cast-off 

 material where they remain scattered until they are fully de- 

 veloped and then become free in the lumen of the tubule. This 

 indicates that the sperms in that stage of development are 

 attracted more by their own thrown-off material than by the 

 rather scanty contents of the nurse cells, which are then very 



