158 Dr. F. A. Dixey on 
may possess, as it always does in the wet season, a 
bright yellow under-surface, hke that of 7. puellaris. 
Simultaneous occurrence of diverse seasonal forms.— 
Attention has frequently been called to the fact that at 
Aden, and probably in other arid districts, “dry,” “ wet” 
and “intermediate” forms may all be found on the wing 
together. Colonel Yerbury remarks with reference to 
Aden that “seasonal dimorphism does not seem to occur 
to any extent in the neighbourhood; though it may 
possibly do so in the case of Zeracolus calais and dynamene.” * 
We may take this to mean, not necessarily that the 
different phases usually associated with different times of 
year are never found at Aden (for the occurrence of some 
of them at that spot is well attested), but that they do not 
there undergo, as in many places, a regular alternation in 
correspondence with the change of season. On the excep- 
tional case of 7’. calais Colonel Yerbury remarks further 
as follows:—‘The year 1883 was very wet, heavy rain 
having fallen in May, consequently in July a large number 
of Butterflies appeared—among others, a very brightly- 
coloured form of 7" calais (all, I believe, females however): 
this may point to 7. calais being the rainy-season form 
and 7’. dynamene the dry. I never met with this unusually 
brightly-coloured form in after years.” 
It may be noted in this record that at least a month 
must have elapsed between the heavy rain and its supposed 
effect on the numbers and aspect of the butterfly fauna ; 
this seems to point (like the facts recounted by Poulton 
for the genus Precis +) to the larval being the susceptible 
stage. On the other hand, the effect of rain may in some 
instances be less remote, as appears from another state- 
ment by Colonel Yerbury,t as follows :—*“ Few passen- 
gers (for the matter of that, no great number of the 
residents) have any idea of the effect on ‘the barren rocks 
of Aden’ of a few heavy showers; how almost immediately, 
as if by magic, vegetation springs up in every ravine and 
watercourse, accompanied by a tolerably abundant insect 
fauna.” In the discussion that followed the reading of 
the author's paper on “ Seasonal Dimorphism ” (Proe. Ent. 
Soe. Lond., March 19, 1902), Colonel Yerbury further ob- 
served that “a temporary rainfall in a dry season in dry 
* Proc. Zool. Soe., 1896, p. 257. 
+ Trans. Ent. Soe. Lond., 1902, p. 457, ete. 
t Journal Bombay Nat. Hist. Soc., vol. vii, 1892, p. 208. 
