Hybridising T. bistortata and T. crepuseularia 37 
number of failures to take place, and yet ultimately for 
success to be obtained. | 
4. The direct hereditary influence exerted by the 
parents is a great one. [In every case in which one of 
the parents was a 7’. ab. delamerensis, there was a large 
percentage of specimens of, or approaching, this form in 
the progeny, and this in spite of my opinion on other 
grounds that 7’. bistortata is the phylogenetically older and 
predominant species. In no case in which typical 7. 
crepuscularia was used as a parent were any forms 
approaching delamerensis produced, although the parent was 
from a brood producing both the typical and melanic forms. | 
5. The older species phylogenetically is more dominant 
in stamping its characters on the progeny. [This is 
probably the same as Standfuss’s statement that the 
phylogenetically older of the parent species is prepotent. 
My view is abundantly proved by the extent of approxima- 
tion (leaving out the direct influence of the ab. delamerensis 
form) towards 7’. bistortata in almost all the broods. This 
approximation is more especially striking in the large 
broods of Dr. Riding, in which delamerensis does not 
enter as a disturbing influence. If, as is here assumed, 
and afterwards attempted to be proved, 7. bistortata 
is phylogenetically a much older species than 7’ ere- 
puscularta, it is evident that the phylogenetically older 
parent leaves more mark on the offspring. It may be, 
of course, that 7’. bistortata is a predominant species, more 
active in its vital functions, and more ready to respond to 
environmental influences, although the variation of 7’. 
crepuscularia renders the latter scarcely probable. At any 
rate, the dominating influence of 7. distortata on the 
progeny is most marked. | 
6. The sex-condition of the hybrids depends on the 
predominating influence exerted by one of the parents. 
[In the reciprocal pairing in which 7’. bestortata is the 
male parent, a fair share of females is the result; when 
T. crepuscularia is the male parent the females are practi- 
cally wanting. This suggests also that the male exerts the 
greater influence in the production of female progeny and 
vice versa. | 
7. A recently formed aberration may be prepotent and 
dominant over the type from which it has but recently 
sprung. [This conclusion appears somewhat paradoxical 
in the face of 5, yet it isevident from these crosses that, 
