166 The Mechanism of Evolutiok in Leptinotaksa 



and in nature it is highly improbable that anything of this sort would happen, 

 owing to the rarity or absence in both of the species of this modal biotype 

 uncomplicated by other conditions or agents productive of other characters in 

 the gametes. No materials direct from nature have ever given any such result 

 entirely, so that natural crosses are more complicated than the one described. 

 Another cross of interest is that between the modal biotype of L. decemlineata 

 that was used in the first instance and L. multitceniatd biotype melanothorax, 

 with other characters those of modal standard. In this combination decem- 

 lineata is dominant in F^ in all stages, especially in the juvenile, and F^ when 

 inbred for F, shows in this instance in the larvas the same array as in the first 

 cross, due to the same causes, and is of no further interest. In the adults, 

 however, there come out in F, sharp indications of the dissociation of the 

 gametic systems, as far as certain adult characters are concerned, showing uni- 

 formly the following types in variable proportions : 



decemlineata in all respects. 



decemlineata with melanothorax pronotum and head. 



multitceniata in all respects of biotype 7. 



melanothorax in all respects. 



multitceniata of biotype 2 aspect. 



decemlineata of biotype 2 aspect. 



Of these there are some decemlineata that breed true ; the majority are hetero- 

 zygous as far as their reactions are known. The decemlineata with the melano- 

 thorax characters has always the form-index of the parent (2.699) and breeds 

 true in part. Multitceniata in all respects of biotype 7 has in all tests bred true ; 

 melanothorax in all respects also breeds true, while none of the remainder has 

 been found to breed true. Out of the combination I have derived thus far the 

 following stable combinations : 



decemlineata in all respects. Eatio, homozygous 3 : heterozygous 8. 



N. = 96. 

 decemlineata with melanothorax pattern ; 4 out of 6 pairs mated. Eatio, 



homozygous 2 : heterozygous 1. N. = 141, 

 multitceniata in all respects of biotype 7; 14 out of 14 tests. Eatio, 



homozygous 1 : heterozygous 0. ]Sr. = 73. 

 melanothorax in all respects ; 12 out of 12 tests. Eatio, 1 homozygous : 



heterozygous. N. = 134. 



All of the other types that come out in Fj do not breed true in any tests thus 

 far made. 



The point of interest in this cross is the crossing of the pronotal-pattern pro- 

 ducing agents from one gametic complex to the other, and this is shown clearly 

 by the finding of them in combination with the characters and form-index of 

 each of the two parent types. Interesting also is the derivation in Fg of multi- 

 tceniata biotype 7 as a result of the cross, showing that the pattern present on 

 the head and pronotum of decemlineata had crossed to and replaced in melano- 

 thorax the corresponding agents, thus synthesizing multitceniata biotype 7 out 

 of the combination, and also giving decemlineata forms with head and pronotum 

 of the melanothorax type. 



None of the juvenile characters have been observed to be dissociated from 

 their respective gametic systems, and in Fj all homozygous forms are red where 



