RECENT EXPERIMENTS IN HYBRIDISATION. 7 



The want of vigour in this cross is shown by the fact 

 that out of nine pairings, each resulting in an average of 

 200 eggs, only ten larvae were produced ; and of these only 

 six, as we have seen, attained the perfect condition. 



7. S.pavonia $ a.nd Ac^zas hma L. ?. Nineapparendy 

 normal pairings took place, and over 1000 eggs were laid; 

 but none of these hatched. 



8. 6*. pavonia $ and A, isabellcB Graells ? . As a re- 

 sult of this crossing, ninety-eight eggs were laid, seven of 

 which hatched. The caterpillars however did not long 

 survive their first change of skin. 



9. 6". bornemanni $ and 5". pyri ? . As 5. bornemanni 

 is the cross-product of S. pavonia $ and 6". spim ? , this 

 hybrid is descended from all three species,^ Only one 

 pairing" was obtained, and 92 per cent, of the eggs hatched. 

 Some of the resulting perfect insects were lately shown in 

 London with the other exhibits of Dr. Standfuss, who 

 promises to publish further details of their history. 



Relative phylogeiietic age of the three European species of 

 Satnrnia. Before stating the general conclusions at which 

 he has arrived as a result of the above series of experiments, 

 the author proceeds to discuss the question of the relative 

 phylogenetic age of the three species Satitrnia spini, S. 

 pavonia and ^. pyri. Of these he considers S. spini to be 

 the oldest form and S. pyri the most recent. His main 

 reasons are briefly as follows : — 



(i) The larva of 5. spini maintains its original black 

 colour throughout its life. ^\ pavonia loses this sometimes 

 in the third stage, always in the fourth and fifth. S. pyri 

 abandons it almost completely in the third stage and on- 

 wards. The succeeding green colour, which is no doubt 

 adaptive, is acquired by S. pyri at an earlier stage and more 

 completely than by 5. pavonia. 



(2) In the larva of 5. spini the tubercles are not very 

 prominent even in the adult, and the knobs at their summit 

 are not distinctively coloured until the last stage. In 6*. 



. ^ Mr. A. G. Butler informs me that an analogous triple cross has been 

 obtained between a goldfinch and the hybrid issue of the English and 

 Japanese greeniinch. 



