No. 509] THE CATEGORIES OF VARIATION 279 



strain disappeared. In other cases the spine was 

 gradually diminished during successive divisions and 

 ultimately disappeared. Other anomalies such as crook- 

 edness, blunt ends, bent tip of body and various abnor- 

 malities, provoked by artificial mutilation, while persisting 

 for a variable number of generations, were eventually 

 regulated out, leaving a normal strain. 



In like manner we may imagine that through environ- 

 mental changes the germ plasm becomes affected by 

 modifications which in the course of a few generations 

 become regulated out, thereby causing a reversion to the 

 primitive stock. Reversion may thus be conceived as but 

 a manifestation of form regulation. Variations to be 

 permanent must be accepted by the organized structure of 

 the germ cells, so that they may be included instead of 

 excluded by the processes of functional equilibration 

 to which these cells like other parts of the organism are 

 continually subjected. The congruity of the variation is 

 the important thing; whether the variation be large or 

 small, sudden or slow, is of much less consequence. 



After all, it may be asked, granting that variations may 

 be interpreted in the manner here set forth, do not the 

 phenomena of Mendelian inheritance, showing as they do 

 that characters may be separated and combined in many 

 different ways prove that these characters must be borne 

 by some sort of units in the germ plasm! This is a con- 

 clusion which is adopted by a large number of Men- 

 delians, but, plausible as it seems, it is, I believe, a totally 

 .erroneous view. In the first place it is open to question 

 if the assumed purity of the gametes is a fact even in 

 typical cases of Mendelian inheritance, but, granting that 

 there is an absolute separation of ancestral tendencies, 

 it by no means follows that there is any sorting of indi- 

 vidual unit characters apart from the complex of tend- 

 encies which make for the production of the organism 

 as a whole. Hereditary anlagen may perhaps be shuffled 

 and sorted as wholes, but if the germ plasm were com- 

 posed of discrete parts representing the unit characters 



