RECENT EXPERIMENTS IN HYBRIDISATION. 187 



to be as usual, and the females contain ova normal in 

 appearance. Their fertility, however, has not been proved, 

 and Standfuss thinks he has reason to doubt it. These are 

 Zygcena trifolii Esp. $ and Z. filipendulce L. ? ; Biston 

 hirtarius CI. $ and B. pomonarius Hb. ?. 



In no single instance, according to Standfuss, has the 

 female of any true hybrid among lepidoptera been shown 

 experimentally to be fertile. Haeckel's counterstatement 

 with regard to the genera Saturnia and Zygoma is probably 

 erroneous. 1 



The most complete series of Standfuss's experiments in 

 hybridisation is one carried on for over ten years with three 

 species of Saturnia, viz., S. pavonia L., 6". spini Schiff, and 

 S. pyri Schiff. The results of these experiments are 

 recorded and compared by their author with great minute- 

 ness, and excellent figures are given by him of several of 

 the resulting forms in their immature and final stages. A 

 brief outline of these records, omitting details, will here be 

 attempted. 



1. Saturnia pavonia $ and .S. spini ?. In this hybrid, 

 called by Standfuss 5". bornemanni, the eggs first laid were 

 regularly deposited, and were fertile to the extent of from 

 60 to 80 per cent. The larvae in all five stages bore a much 

 closer resemblance to those of 6". spini than to those of S. 

 pavonia, though this became less pronounced after the 

 second stage was passed. The cocoon and pupa were both 

 intermediate in structure, but the perfect insect was nearer 

 to 6". spini than to S. pavonia. This applies to both sexes, 

 but is more easily seen in the male, the males of the two 

 parent species differing (as is usual) more than the females. 



2. The reciprocal cross (S. spini c? and S. pavonia ? ; 

 = 6". hybrida Ochs.) has not been produced in captivity, 



1 Standfuss does not notice the case cited from Quatrefages by Wallace 

 {Darwinism, 1889, p. 163), of fertility inter se in the hybrids between 

 Bombyx cynthia and B. arrindia. Fletcher also has obtained fertile 

 hybrids of both sexes between Zygcena /onicene Esp. and Z. trifolii {Proc. 

 Ent. Soc. Land., 1893, p. ix.). On the other hand, the hybrids of 

 Z. lomcerce and Z. filipendnhe proved infertile {Ibid., 1S91, p. ix.), and the 

 hybrid progeny of various species of Platysamia and Actias were found by 

 Miss Morton to be sterile in both sexes {Ibid., 1895, p. xxxiv.). 



