EXPERIMENTS IN HYBEIDIZATION AND TEMPERATURE. 343 



some respects stronger than the male of the same form (see 

 Handb. 1896, pp. 220-226, and PI. IV. figs. 5-17, and PI. V.). 



The followmg is shortly the result of the experiments made 

 by the author up to the end of 1894 : — 



I. The biological character of the primary hybrids, as was 

 very clearly proved in the habits of the Saturnia hybrids (see 

 Handb. 1896, p. 83), is principally influenced by the special pecu- 

 liarities of the phylogenetically older species. 



II. The morphological character of these hybrids is deter- 

 mined by two factors. 



The first and most important is the inclination of the offspring 

 to follow the phylogenetic oldest form. As subordinate to this 

 first law, the predominant influence of the male parent. (This, 

 however, appears not always to be the rule.) 



III. The physiological character in a sexual direction was 

 shown by anatomical research to be as follows : — 



The females of five of the hybrids obtained (a further sixth 

 form yielded only males) possessed either none at all, or else 

 very few degenerate egg-germs or eggs, and the latter have as 

 yet never shown themselves capable of development. 



All these hybrids were therefore, without doubt, incapable of 

 reproduction. 



Only the females of the seventh cross {Zygana trifolii, Esp., 

 ^ xfilipendul(B, L., ? ) constantly had in their ovaries a large 

 number of apparently normally formed eggs, the powers of whose 

 development have unhappily not yet been ascertained. The male 

 hybrids, however, were no doubt all capable of reproduction ; 

 this was indicated by an anatomical dissection of the repro- 

 ductive organs of a number of them. 



The experimental test of the reproductive capabilities of male 

 hybrids, when crossed back with females of both parent forms, 

 showed that the fertility of these primary hybrids was greater 

 when paired with the phylogenetic older form than with the 

 phylogenetic younger ; so that the physiological characters of 

 the primary hybrid were nearer to the phylogenetic older form 

 than the younger. 



Further trials were made in the years 1895-7 in the direction 

 of more thoroughly testing the characters of the various hybrid 

 forms. 



As previously, our three Central European Saturniids— sj?mi, 

 pavonia, and pyri, and their hybrids — were used. 



The result is systematically shown on the accompanying 

 plan. (See p. 344.) 



As will be seen, not only the hybrid males of the crossing of 

 S. pavonia $ x ^pini ? No. 8 (cfr. Handb. 1896, PL II. figs. 3, 4, 

 5), but also of the crossing of B. pavonia $ x pyri ? No. 9 (cfr. 

 Handb. 1896, PI. I. figs. 1-4) could be crossed back with the 

 parent species, and imagines from all these four crossings 



2g2 



