160 Dr. F. A. Dixcy on 



The foregoing may perhaps help us towards an explan- 

 ation of the well-attested facts relating to the simultaneous 

 occurrence of seasonal forms in generally dry localities 

 like Aden. A feature in Colonel Yerbury's graphic 

 description of a temporary rainfall and its effects is the 

 rapid springing-up of vegetation and the accompanying 

 increase of insect life. As Professor Poulton has shown, 

 these are the exact conditions Avhich allow of the assump- 

 tion of aposematic colouring and habits in exchange for 

 those of a cryptic character. Now if we assume, as it 

 seems from Colonel Yerbury's observations we ma}^, that 

 many of the Aden species are in a condition to respond 

 almost immediately to a sudden access of moisture, the 

 occurrence of the more conspicuous "wet-season" con- 

 temporaneously with the cryptic "dry-season" forms 

 receives some explanation. Where there is a regular 

 alternation of long periods of drought and humidity, the 

 seasonal phases of the insect fauna fall into a corres})ond- 

 ing regularity of succession ; but where, as at Aden, a 

 general state of aridity is liable to be occasionally dis- 

 turbed by heavy rainfalls of a temporary character, the 

 intermittent meteorological conditions are apt, we may 

 suppose, to be reflected in a similar intermixture of apose- 

 matic and cryptic forms of insect life. It would not be 

 difficult for residents in such localities to test the 

 suoo'estion here offered.*' 



Note on Teracolus daira and T. evagore, King. — Dr. 

 Butler, in his "Revision of the Genus Tcraculufi" (Ann. 

 Mag. Nat. Hist., 1897), distinguishes Teracolus ycrhurii, 



the usual mile as to the superiority in weight of tlie »:si(mns form 

 did not oLtain in the instance of Mr. Marsliall'.s P. aemvuis and P. 

 uatidensis hred from two eggs laid by the same mother. The weights 

 as determined by Professor Poulton (Trans. Ent. Soc. Lond., 1902, 

 p. 451) show that in this case the natalcnsis form was the heavier of 

 the two. Whatever then may have been the influence which caused 

 the diversity between the two offspring, it did not find expression 

 in any increased bulk of the fiesamus larva. It should also be borne 

 in mind that the larval conditions of the first dry- or wet-season 

 brood will probaldy differ from those of the second and subsequent 

 broods (should there be more than one) of the same .season. 



* See ]Mr. G. A. K. Marshall's account of the simultaneous flight 

 of different seasonal phases during an abnormal season in Mashona- 

 land (Ann. Mag. Nat. Hist., 1901, vol. ii, p. 402), and compare the 

 discussion of the succession of seasonal phases in Precis by Pro- 

 fessor Poulton and Mr. Marshall in Trans. Ent. Soc. Lond., 1902, pp. 

 443-449. 



