202 THE PERPETUATION OF ADAPTATIONS 



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 successive 

 outposts of advance. 



C. CONFORMITY TO TYPE 



A female lobster produces thousands of eggs each of which af- 

 ter 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 experi- 

 ment 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 organ- 

 ism 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 organisms 

 similar to the parents and when and how did changes occur? 

 It is the old problem of the hen and the egg; the egg came first 

 but the hen gradually evolved from generalized ancestral forms 

 quite dissimilar from the modern fowl. How were the successive 



