SPERMATOGENESIS OF THE PIG. 3! 



23. The axial envelope which extends a little more than half 

 the length of the tail is developed from the cytoplasm. 



24. The half developed spermatozoa attach themselves to 

 Sertoli cells where they continue to develop. 



25. The cytoplasmic mass of the Sertoli cells decreases greatly 

 in size as the spermatozoa continue to develop. Finally, when 

 the spermatozoa are almost mature, a collapse of the nurse cells 

 takes place when practically nothing but the nucleus and the 

 cell wall remain. 



26. An interesting event occurs in the final stages of the devel- 

 opment of the spermatozoan when a large mass of cytoplasm 

 together with the posterior centrosome is thrown off by the cell. 



27. When the spermatozoa desert the Sertoli cells they do not 

 pass directly into the lumen of the tubule but remain scattered 

 with their heads embedded in the layer of the cast-off cytoplasm. 



28. The cast-off cytoplasmic material is apparently used as 

 food by the maturing spermatozoa and when practically all of the 

 former disappears the fully developed spermatozoa become free 

 in the lumen of the tubule. 



29. Measurements of the mature spermatozoa reveal the fact 

 that they are of two distinct sizes, a point no doubt correlated 

 with the presence and absence of the accessory chromosomes. 



30. The somatic cells of the male contain eighteen chromo- 

 somes, a number corresponding to that in the spermatogonia. 



31. The somatic cells of the female yield a count of twenty 

 chromosomes as do the oogonia. 



32. The foregoing facts add considerably to the support of 

 the chromosome theory of sex determination, since they prove 

 that in the vertebrates, as is true of some invertebrates, there 

 exists a dimorphism in the germinal and somatic cells of the male 

 and female. 



LITERATURE CITED. 

 Allen, B. M. 



'04 The Embryonic Development of the Ovary and Testis of the Mammals. 



The American Journal of Anatomy, Vol. III., No. 2, pp. 89-153. 

 Guyer, M. F. 



'oo Spermatogenesis of Normal and of Hybrid Pigeons. Dissertation: Univer- 

 sity of Chicago, 1900. 



'oga The Spermatogenesis of the Guinea. Anat. Anz., Bd. XXXIV., Nr. 20. 

 The Spermatogenesis of the Domestic Chicken. Anat. Anz., Bd. XXXIV., 

 Nr. 22. 



