G. Vererbungslehre. 157 



and hybridized, in order to learn what the results would be if two 

 spezies sbould come in contact under different conditions, and 

 hybridize, and these results I shall describe under the head of Experiments 

 in Synthesis." 



The general results are indicated on page 332 as follows: 

 „The chief variables in these experiments vvere the conditions surrounding 

 and incident upon the germ cells at the time of fertilization. All of the 

 crosses herein recorded were made between individuals of the sarne age and 

 always between vigorous individuals of their respective population; that is, the 

 materials for crossing were always homogeneous as far as could possibly be 

 determined, and I never mated an old male with a young female, or vice versa. 

 In these experiments I have succeeded in creating a series of behaviors 

 in which the same characters are dominant to the complete exclusion of the 

 others; dominant to a lesser degree, or in which there is a complete blend 

 between the two in the Fj generation, or the appearance of both parental 

 types in F 1 and both breed true. As far as it has been possible to deter- 

 mine, the only variable in these experiments is that stated, and I am led to 

 the conclusion that the conditions surrounding and incident upon the germ 

 cell at the time of fertilization may be to a very considerable extent respon- 

 sible for the determination of the dominant character in the cross and largely 

 responsible for variability of such characters." 



Tower's conclusions are given on pages 335 and 336 in the following 

 quotation: 



„The experiments and observations herein given Warrant the general State- 

 ment that conditions external to a cross are important factors in determining 

 the results thereof. This conclusion has been worked out in both normal 

 and hybrid crosses, in crosses between races which have been created selecti- 

 vely, and between forms which arose as sports; and the second series of ex- 

 periments in synthesis is sufficient Warrant for attributing to this factor a 

 considerable importance in evolution. 



Underlying these, there are, of course, deeper factors than those with 

 which we are dealing. Tbe characters which behave Mendelian wise are in 

 the main superficial, unimportant attributes of the organism, and only rarely 

 are they the characters which would make for success or failure in the 

 struggle for existence; they are most often color and specific characters, which, 

 while fixed and vigorous in their behavior, are not important in the economy 

 of the organism. These behaviors, beyond any question as to how and why, 

 suggest the Operation of something which gives a result best described at 

 present in factorial terms; and that there are such things as later onto- 

 genetic factors seems highly probable in many cases and absolutely certain as 

 regards many colors. The knowledge that we have concerning melanogenesis 

 leaves us no alternative in this respect. 



Back of all this, however, is the fundamental question of how these germ 

 cells, how this living substance is constituted, and what is the relation in this 

 complex of that which makes for the elaboration of tyrosin and tyrosinage in 

 melanogenesis. What is it in this complex that localizes in a definite area 

 the appearance of a pigment? What is it that combines into a definite 

 pattern, a series of attributes, some of which can be shifted and rearranged 

 in the processes of hybridization? The problem of the constition of the ga- 

 metes of that which makes for form, for localization, for pattern, etc., is the 

 fundamental problem; aud as long as we fail to see clearly what the Con- 

 stitution of living matter is, such phenomena as these which we have been 



