EVOLUTION 207 



in the different fields of experimental zoology, botany, embryol- 

 ogy, and genetics introduced many new problems for solution, 

 while the attempts to solve them threw a brilliant flood of light, 

 not only on the old question of evolution, but over the entire 

 field of biological phenomena. Indeed, it may be safely stated 

 that all of the great strides in modern biology have been along 

 the lines marked out through use of experimental methods. 



The greatest of these strides has been taken along the line of 

 heredity or genetics, and a new point of view of the origin of 

 variations has resulted. It is not the work of any one man, 

 nor has the advance always been definite, but certain names 

 stand out prominently, and certain achievements mark succes- 

 sive outposts of advance. 



C. CONFORMITY TO TYPE 



A female lobster produces thousands of eggs, each of which, 

 after fertilization, has the potential of a new adult lobster, and 

 all of the brood are essentially similar to one another . and 

 similar to those produced by other lobsters. If one or more 

 claws of two parent lobsters are cut off early in life and kept cut 

 off after successive regenerations, the fertilized eggs resulting 

 from these two individuals will develop again into normal adult 

 lobsters with perfect appendages. I am not aware that such an 

 experiment has actually been made with lobsters, but it has 

 been worked out in so many other cases that we are justified in 

 assuming the result with these Crustacea. The main point is 

 that the visible changes or defects of the parents have no 

 apparent effect on the eggs and embryos produced by them. 

 In other words, the germ cells conserve the particular type of 

 organism producing them, not necessarily that of the immediate 

 parents, but of the race to which the parents belong. 



If the various types of Crustacea which are known today have 

 had common ancestral forms in some more generalized type, 

 why did not the eggs of that generalized type produce organ- 

 isms similar to the parents, and when and how did changes 

 occur? It is the old problem of the hen and the egg; the egg 



