GERM-CELL HISTORY IN THE BROOK LAMPREY 81 



partition of chromatin material during cell mitoses or to an 

 unequal distribution of cytoplasmic material during the early 

 divisions of the cells. Just as the germ cells are set aside from 

 the somatic cells in early stages of development by some differ- 

 ences in their make-up, so the germ cells may also differ among 

 themselves in their inherited structure after each division. There 

 is direct proof that there is an unequal distribution of material 

 among the cells in early stages of some animals, and that certain 

 cells are destined to form certain parts of the body. These dif- 

 ferences appear to be cytoplasmic in most cases; for example, in the 

 case of Cynthia, in which (Conklin, '05) there are several kinds 

 of organ-forming substances which are unequally distributed 

 among the cleavage cells. In later stages, however, there is no 

 direct proof of an unequal division of the cells ; so in the case of the 

 germ cells of the lamprey it must remain an assumption that 

 unequal division does take place; but this would explain the two 

 types of behavior of the germ cells. 



Again the germ cells might all be assumed to have the same 

 inherited structure, and yet they may develop along different lines 

 on account of their different local environment in the gonad. In 

 this case the behavior of the cells would be the result of factors 

 or circumstances acting from without. These factors may be 

 supposed to be differences in nutrition, the presence of various 

 enzymes and toxins, differences in pressure, and various other 

 factors operating in the germ gland of the animal. In this case 

 it must be assumed that the germ cells are so constituted that they 

 can respond to environmental factors in two different ways. 

 Under certain conditions the cells will continue to divide, under 

 others they will stop dividing and enter upon a period of growth. 



As yet we know too little about the physiology of the cell to be 

 able to decide between the two possibilities. We know that in a 

 form hke the lamprey, whether it eventually becomes a male or 

 a female, the two kinds of cells make their appearance, some 

 with a tendency toward rapid division and some with a tendency 

 for growth. Now, since the latter is an undoubted female quality 

 and the former is supposedly a male quality, practically every 

 individual must possess both male and female potencies. That 



