840 THE ENTOMOLOGIST. 



SYNOPSIS OF EXPERIMENTS IN HYBRIDIZATION AND 

 TEMPERATURE MADE WITH LEPIDOPTERA UP TO 

 THE END OF 1898.- 



By Pkof. Dr. Max Standfi^ss. 



Plates III. & IV. (Eutom. Plates VII. & VIII.). 



(Continued from p. 292.) 



Second, Crossing, and Hybridization Experiments. 



The increase in numbers of species is caused by the splitting 

 up of a group of individuals which originally lay within the 

 limits of a single species, the separated forms becoming more 

 and more divergent till quite isolated. This is a generally 

 accepted theory of zoology. 



If we name the groups of individuals which are diverging 

 A and B, this isolation manifests itself through the fact that 

 neither A 3" crossed with B ? nor B <? with A $ are capable of 

 producing offspring which are sufficiently fertile to remain as 

 an independent form, even for a — phylogenetically speaking — 

 limited period. 



This isolation must be regarded as the final result of a con- 

 tinued increasing physiological divergence and difference, and 

 we must accept this as the cause of creation of species for all 

 geological periods of our earthly fauna and flora. 



If this theory is correct, the artificial crossing experiments 

 will indicate the present state of the physiological divergence and 

 difference of the creatures and plants experimented with. The 

 following hybridization experiments with Lepidoptera — which, by 

 the way, are very difficult — were undertaken with this idea, and 

 with this end in view ; and to me it appears that none of the 

 results obtained reduce this theory ad absurdum, but, on the 

 other hand, prove its validity. 



Of the numerous hybridization experiments made during the 

 years 1873-1894, many had a constantly sterile result, in spite 

 of frequent repetition. 



Nine different crossings of genuine species were fertile : — 



1. Smerinthus ocellata, L., S x 'populi, L., ? . 



2. Zygcena trifolii, L., <? xjilipendulce, L., ? . 



3. Bomhyx franconica, Esp., <? X castrensis var. veneta, 

 Stdfs., ? . 



4. B. castrensis var. veneta, Stdfs., <s x franconica, Esp., ? . 



5. B. neustria, L., 3' x franconica, Esp., ? . 



6. B. neustria, L., <? X castrensis var. veneta, Stdfs., ? . 



7. Saturnia pavonia, L., <y x Actias isabella, Grsells, ? . 



8. S. pavonia, L., 3 X spini, Schiff., ? . 



9. S. pavonia, L., 3 xpyri, Schiff., ? . 



