154 Experimental Zoology 
being exceedingly rare and almost confined to South Wales, but 
that of T. crepuscularia is widely distributed and known as 
aberratio delamerensis. The first generation of hybrids (F,) 
is described as containing individuals that are like the one or 
the other parent form, although each kind may show traces of 
the other species. Tutt states that he has avoided the use of the 
term ‘intermediate’? when describing these hybrids because the 
term has been made to cover so many different things; but that 
nevertheless all of the hybrids with few exceptions are inter- 
mediate to varying degrees, 7.e. ‘almost every specimen appeals, 
in some part of its facies, to a specialist, as resembling T. bis- 
tortata, whilst the same specimen, in other particulars, strikes 
one as resembling T. crepuscularia.’”’ When inbred the hybrids 
produce a large percentage of individuals differing much from 
either parent-form. The crossing of the hybrids, obtained 
from original reciprocal crosses, tends to produce a mixed prog- 
eny, some referable to known forms of the crossed species, 
others quite unlike anything ever obtained in nature. . . . These 
experiments support Eimer’s view that sexual combination can 
lead to the production of new forms. I doubt, however, very 
much whether they could be perpetrated without selection,” 
for if crossed with one of the present species they would “in my 
opinion”’ revert to the wild form. 
Some interesting results were also obtained in regard to the 
sex of the hybrids. “The greater vigor of the male results 
largely in the production of female offspring. When the male 
is of the dominant species, females are developed in fair propor- 
tion; when the female is of the dominant species, males are 
largely in excess.” 
LITERATURE, CHAPTER IX 
Couracne, G. Recherches experimentales sur ’hérédité chez les vers 
4 soie.. Bull. Sci. France et Belg. XXXVII. 1902. 
Sur les facteurs élémentires de Vheredite. Comp. Rend. Acad. Sci. 
Paris, CXXXVII._ 1903. 
Sur les croisements entre taxies differentes. Comp. Rend. Acad. Sci. 
Paris, CXXXVII. 1903. 
