66 Inheritance of Melanism in Tephrosia (Ectropis) 



order as that seen in the allied Boarmia consortaria, the melanic forms 

 of both insects are sharply discontinuous from the types. 



(4) Object of the experiments. 



With the enumeration of these facts we are brought to the stage 

 when the exact purpose for which the present research was undertaken 

 may be revealed. In all of my previous work on the genera Nyssia, 

 Lycia, Poecilopsis, Ennomos, Drepana and Platysamia it has invariably 

 happened that,' when dealing with interspecific and interracial crosses, 

 the phenomenon of blending inheritance was encountered, and when the 

 hybrids proved fertile there was a persistence of the blend in the F2 

 and subsequent generations. On the contrary, in intraspecific crosses 

 between aberrant or mutational forms and the type of any species 

 ordinary Mendelian behaviour has been displayed. Naturally enough, 

 therefore, in my mind, as in others, the thought has been engendered 

 that the former type of inheritance might be typical of crosses between 

 species, and that the latter was equally proper to crosses between dis- 

 continuous varieties of the same species. 



In the material discussed above we have an excellent opportunity of 

 putting these views to the test. We have two species, each with its own 

 peculiar melanic form, which are not only fertile when cross-paired but 

 yield progeny likewise fertile, either when mated inter se or when back- 

 crossed with either parent species ; and this fertility of the hybrid 

 generations continues as long as their inbreeding is continued. By the 

 introduction of melanism into crosses involving only one species, as well 

 as into crosses between Tephrosia bistortata and T. crepuscularia, we 

 can see whether its behaviour during crossing in these species supports 

 our opinion or not. The exact question propounded for solution then 

 becomes : Is the inheritance of melanism in both cases on typically 

 Mendelian lines, or is it in the one case Mendelian and in the other 

 blending ? 



(5) Observations concerning the material and technique. 



Partly to render the experiment more manageable by restricting the 

 number of broods, and partly owing to the uncertainty of securing 

 regular supplies of ova of T. bistortata var. passetii, it was determined 

 to introduce the melanism solely by means of the species T. crepuscu- 

 laria, and to do this insects almost pure black in tone, save for the white 

 subterminal band, derived from pure breeding stock, were employed. 

 Strictly, of course, to be in accord with modern nomenclature this 

 variety ought to be regarded as belonging to var. nigra Thierry-Mieg. 



