158 Dr. F. A. Dixey on 



may possess, as it always does in the wet season, a 

 bright yellow iinder-surface, like that of T. imcllaris. 



Swiultaneous occurrence of diverse seasonal forms. — 

 Attention has fre(|nently 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 Teracolus Calais and dynam.ene." * 

 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 T. Calais Coloneb Yerbury remarks furthe]- 

 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 T. ccdais (all, I believe, females however) : 

 this may point to T. Calais being the rainy-season form 

 and T. dynamcne 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 f) 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,:J: 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 " (Proc. Ent. 

 Soc. Lend., March 19, 1002), Colonel Yerbury further ob- 

 served that " a temporary rainfall in a dry season in dry 



* Proc. Zool. Soc, 1896, p. 257. 



t Trans. Ent. Soc. Lend., 1902, p. 457, etc. 



X Journal Bombay Nat. Hist. Soc, vol. vii, 1892, p. 208. 



