30 IOWA ACADEMY OF SCIENCES. 



name. Germ plasm is the name given to the material of 

 the germ in which heredity resides. As the germ devel- 

 opes this material controls the development by dividing up 

 for the most part, and passing out into the different parts 

 of the body to form the protoplasm of the body, or the 

 somatoplasm, in a manner that we may suppose to be the 

 same as that by which a mass of gemmules in the theory of 

 pangenesis accomplishes the same purpose. But, and here 

 is the essential part of the theory, a portion of the germ 

 plasm does not take part in this process, but is reserved; 

 that is, it does not come into activity in controlling the 

 development of that particular germ, but is simply passed 

 along unchanged in a certain chain of cells that ulti- 

 mately lead up to and form the reproductive glands. 

 When certain cells of these glands become germ cells, the 

 germ plasm is therefore already a constituent of them. 

 The theories of pangenesis and of the continuity of the 

 germ plasm do not therefore necessarihj differ in the rela- 

 tion between the material basis of heredity and the devel- 

 opment of the individual, but they are diametrically 

 opposed as to the source of this material basis of heredity 

 in each generation. Pangenesis supposes that the germ 

 plasm is newly formed in each generation; the other 

 theory that it is passed on ready formed from generation 

 to generation — that is, that it is continuous from genera- 

 tion to generation. 



While the character of the somatoplasm is determined 

 by the germ plasm, since it arises from it during develop- 

 ment in each generation, the structure of the germ plasm 

 is not in a reverse manner determined by the somatoplasn», 

 since the germ plasm is not produced by the somatoplasm, 

 but is simply handed along from the preceding generation. 

 It must not be understood that changed conditions to 

 which the individual is subjected cannot at all influence 

 the germ plasm, for of course the latter is dependent on 

 the rest of the body for its nourishment, and anything that 

 interferes with the proper supply of this, in kind or quan- 

 tity, must affect both somatoplasm and germ plasm. But 

 there can be no representative changes produced in the germ 



