564 Gideon S. Dodds. 



Introduction 



The study of the segregation of the germ-cells is of interest 

 from two points of view; first, in relation to the general stud}'' of 

 problems of heredity; and, second as a part of the problem of 

 embryonic differentiation. 



The mechanism by which the qualities of one generation become 

 repeated in the next has long been a subject for speculation and 

 investigation. The more recent views of the separateness of 

 germ plasm from somatic structures receive their verification or 

 refutation from studies of the actual separation of the germ-cells 

 and body cells in the early developmental stages of the individual. 

 The segregation of the reproductive cells in early development 

 would establish a continuity between the germ-cells of succeed- 

 ing generations without the intervention of the specialized tis- 

 sues of the animal body. 



In relation to the mechanism of cell differentiation the phenom- 

 enon is of further interest. In the history of both the race and the 

 individual, the separation of the reproductive from the vegeta- 

 tive cells may be the earliest differentiation. It is this setting 

 aside of generalized cells to transmit the characters of the race 

 that allows the remaining cells, when relieved of this responsi- 

 bility, to undergo the high degree of differentiation found in the 

 body of the higher animal and plant. The problem of the differ- 

 entiation of the germ-cells is not different from that of cell special- 

 ization in general; it is but the beginning of the longer, more 

 general process and as such may be conditioned by the same fac- 

 tors. An understanding of the differentiation of the germ-cells 

 is the first step toward a comprehension of the general embryonic 

 differentiation that follows. 



The present investigations on Lophius piscatorius have to do 

 chiefly with the earlier stages and were carried on at the zoological 

 laboratory of the University of Pennsylvania, and in part at the 

 Marine Biological Laboratory, Woods Hole, Mass. The prob- 

 lem was suggested by Prof. Thomas H. Montgomery, Jr., to 

 whom I am indebted for many helpful and stimulating sugges- 

 tions. For certain preserved material I am further obligated to 



