224 EDWIN G. CONKLIN. 



development of egg fragments may be the result of regenerative, 

 or regulative, processes. It is not usually possible to connect 

 definite modifications of the adult with definite alterations of the 

 germ from which it developed, but one remarkable instance in 

 which this is possible is found in cases of inverse symmetry. In 

 sinistral gasteropods, and p'resumably in all other cases of inverse 

 symmetry, the cause of inversion is to be found in the inverse 

 organization of the unsegmented egg and I have elsewhere (1903) 

 shown reason for believing that this may be due to the matura- 

 tion of the egg at opposite poles in dextral and sinistral forms. 

 Here one of the most sudden and profound alterations of structure 

 with which we are acquainted may be traced back to a specific 

 modification of the germ. 



These facts point to the conclusion that the complex organ- 

 ization of an egg, such as that of an ascidian, has not arisen 

 through the "reflection of adult characters upon the egg," but 

 rather that this organization is primary. Furthermore they 

 seem to indicate that evolution has taken place, not through 

 modifications of adult structure, but through changes in germinal 

 organization ; modifications of this organization, however pro- 

 duced, are probably the real causes of evolution. 



This conclusion, which has grown out of a study of the com- 

 plex organization of the germ and its relation to adult organiza- 

 tion, harmonizes entirely with the mutation theory of DeVries ; 

 it indicates how mutations in elementary germinal characters may 

 appear as widespread modifications in the mature organism ; it 

 offers an explanation of otherwise inexplicable variations of adult 

 structure, such as inverse symmetry ; and finally it suggests a 

 possible solution of that vexed problem of the origin of phyla, 

 not by the transmutation of one adult form into another, as is 

 assumed in all previous hypotheses, but by relatively simple 

 alterations of the type of germinal organization. 



UNIVERSITY OF PENNSYLVANIA., PHILADELPHIA, 

 December 30, 1904. 



