Eeactions and Pkoducts in Interspecific Crosses 



101 



either in nature or in experiment, and may be, therefore, regarded as the results 

 of aberrations induced by incident conditions during ontogeny or as the result 

 of small numbers observed, the modal divergence in different years being purely 

 a chance one. 



The inheritance of the form-index and its behavior in crossing is shown 

 graphically in figure 5, where the products of three crosses are shown between 

 these two species, as well as the fraternities from which the parents of each 

 cross came. Modal individuals were used for the matings in each of the three 

 shown. From figure 5 and table 5 it is seen that the F^ heterozygotes are in 

 modal position between the modes of the parent species, are intermediate in this 

 respect, although the exact position of the mode upon the scale of values differs 

 in different fraternities, and the range of the polygon in all instances overlaps 

 that of the parents to a varying extent. 



Table 5. 



Matings of the heterozygotes show uniformly in Fg that the visibly segre- 

 gated products are also segregated with respect to the form-index, and that 

 the form-index of L. diversa is in all instances associated solely with the more 

 easily visible characters of that species, and that none of the individuals with 

 this index carries signaticollis characteristics; the same is also true of the 

 extracted signaticollis type, in that it is entirely associated with signaticollis 

 characters. The mid-types, or heterozygotes, in their mode and distribution, 

 are always in an intermediate position, and individuals from this polygon always 

 give in F, the same behavior as is found in the progeny from the F^ hetero- 

 zygotes. In other words, there is complete segregation of the form-index as 

 well as of all of the characteristics that accompany it in the parent species, and 

 no evidence has thus far been discovered in these normal crosses of the inter- 

 change of any characteristics between the two gametic systems as the result of 

 passing through this normal crossing reaction. 



The point of special interest is the behavior of the gametic system species as 

 a unit in crossing under the conditions of the experiment, and the non-dissocia- 

 tion of it in any portion of the series. There are present the two basic species 



