MALE REPRODUCTIVE CELLS 423 



GROWTH AND DEVELOPMENT OF THE MALE REPRODUCTIVE 



CELLS 



The first stages of a male reproductive cell are represented, as are 

 those of the female, by a rather larger and clearer mesodermal or ecto- 

 dermal cell, which stands out from its fellows and must be identified 

 by its position and the surrounding tissues rather than by its structure. 

 Unlike the early ovum this cell has no great amount of food to store 

 up in its body during the first part of its development. Certain of its 

 fellows, however, are differentiated at an early period to act as nutri- 

 tive cells to it during the last part of its development. As in the female, 

 they are termed the nurse cells or, sometimes, the Sertoli cells. 



The male reproductive cells are, at first, scattered through the future 

 gonad or on its surface. As development advances they segregate into 

 groups which are either rounded masses or elongate rod-like regions, as 

 for instance the seminiferous tubules of mammals. We shall call these 

 groups, irrespective of their shape, the spermatic lobules. As the sperm 

 cells ripen the lobule either acquires a duct which conducts the semen 

 away or else it ruptures and discharges its ripe contents into a body 

 cavity or out into the surrounding water. 



Most of these lobules are solid masses while the reproductive cells are 

 young, and some of them continue so until the sperm is ripe and ready 

 to be discharged, when the entire mass is allowed to flow into the sperm 

 channels by the rupture of the lobular wall. Other lobules, which are 

 solid at first, later acquire a lumen. It is only when the spermatozoa 

 are beginning to mature that the lumen appears in the center. The 

 presence of this lumen leaves the reproductive cells which line the lobule 

 lying in a single or, more often, multiple row on the capsule, and we 

 shall hereafter refer to them in this condition as the reproductive epithe- 

 lium. This reproductive epithelium is further divided, in practically 

 all testes of well-differentiated animals, into a series of cell groups which 

 are of greater significance and more fundamental in character than the 

 lobule. The lobule is more properly an anatomical feature, sometimes 

 small, as in most Crustacea, and largest perhaps in some of the mammals, 

 where it forms the long seminiferous tubules mentioned above. These 

 more fundamental groups of male reproductive cells, which we shall 

 call the sperm columns, are smaller groups based upon some nutritive 

 relations to the nurse cells. They are also determined probably by the 

 time that some particular group of spermatogonia initiates the matura- 

 tion process. The sperm column is usually associated with a single 

 nurse cell or Sertoli cell, although it may rarely have more than one such 



