80 



THK ENTOMOLOGIST. 



females had distributed in the breeding-cage masses of eggs, 

 which seemed to be normally constructed, and whose capabilities 

 of development should be proved. How are these curious results 

 to be explained ? 



The fact, that in our experiments the male Pygcera hybrids 

 develop much quicker than their sister females, and that the 

 male hybrid immediately produces a big third generation of 

 males, indicates a progressive developmental tendency, which is 

 further confirmed by other facts. But above the tendency to 

 progressive development in a biological and morphological 

 direction, is the law again to the fore among these Pygseras, 

 that the characters of the oldest pliylogenetic species are im- 

 pressed upon the offspring ; we will, however, not reiterate this 

 question. 



On the other hand, with regard to the females of the Pygcera 

 hybrids, they later endeavour to return to the original simple one 

 generation during the year (for this was certainly the primitive 

 condition). This state comes about sometimes directly; and, 

 moreover, the females of this hybrid form, both as larvae and 

 imagines, revert to a greater degree than the males to the oldest 

 phylogenetic form. 



It is quite a common character of the Lepidoptera (of 

 which I have mentioned several important facts in my Hand- 

 book) that the male individuals have a well-marked tendency to 

 progression, and to the creation of new forms ; whereas the 

 females are more conservative, and, in some cases, show a 

 tendency to retrogress. If we now regard the hybrids, who, in 

 comparison with individuals of pure origin, must be conceded 

 to have a greater freedom and individuality in their evolution, 

 their development is not influenced by the junction of two germs 

 which are pushing forward in the same direction, but by the 

 junction of influences pushing in two opposite directions : in the 

 male sex a tendency to development in a definite and progressive 

 direction ; in the female, an opposing tendency to retrogress. 

 The tendencies directing development, which are here forced 

 upon our notice, are no doubt inherent sexual peculiarities, or, 

 as we may well say, sexual characters which have become 

 constitutional. Unfortunately we can only give a passing notice 

 to this extraordinary fact. 



From these new hybridization experiments we have, firstly, 

 filled the gap in our former hybridization experiments.^*^ There' 

 have now actually been found, from three diflerent crossings, 

 primary hybrid females which are apparently normally formed, 



16 As will be seen in footnotes 11 to 14, the crossing experiments with 

 Drepana falcataria and curvatula, and with Pygcera jJ^V/ra, Hfn., curtula, 

 L., and anachoreta, F., were repeated in 18ii8. Not only these, but a 

 number of new experiments were added to those already made with the 

 Bombycid species. 



