— i8i — 
III. — Section D’Évolution et Mimicry. 
(Séance supplémentaire.) 
a. M. F. Merrifield (Brighton) : Experimental Entomology. 
b. M. W. Schaus (Londres) : A quoi sert le Mimétisme ? 
Discussion : Prof r M. Seitz (Darmstadt), R. Trimen (Woking), 
Hon. W. Rothschild (Tringl Prof r E.-B. Poulton (Oxford), 
D r F.-A. Dixey (Oxford), G.-A Marshall (Londres). 
Président : M. le Profs Poulton (Oxford). 
Vice-Président : M. Trimen (Woking). 
Secrétaire : M. F. Ball (Bruxelles'. 
Le Vice-Président annonce qu’il a fallu constituer cette séance 
supplémentaire consacrée surtout au mimétisme, le nombre et 
l’étendue des communications présentées à la séance précédente 
n’ayant pas-permis d’épuiser le siqet. 
M. Primen donne la parole à M. Merrifield qui parle de : 
On factors in seasonal dimorphism. 
{Résumé.) 
A large and varied number of experiments had satisfied him that 
a low temperature in the early part of-larval life, followed by a 
higher temperature in the later part of it, in A. levano, produced 
the summer phase with its short pupal period, and the reversed 
treatment produced the winter phase with its long pupal period. 
In 6’. b Unitaria it was the same, and here the winter phase larva 
seemed to have one more change of skin than the summer phase 
larva, and was regularly from 30 to 40 per cent heavier. Phere was 
no congenital tendency to alternation of phases; either phase could 
by temperature applied at the proper period of larval life be con¬ 
verted into the other. (Vol. II, Mémoires, p. 433.) 
M. le Profi Poulton (Oxford) prend la présidence et remercie 
