160 Dr. F. A. Dixey 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 which 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 may, 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 fanna fall into a correspond- 
ing regularity of succession; brt 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 reflecte din 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 
suggestion here offered.* 
Note on Teracolus daira and T. evagore, Alug.—Dr. 
Butler, in his “Revision of the Genus Zeracolus” (Ann. 
Mag. Nat. Hist., 1897), distinguishes Zeracolus yerburit, 
the usual rule as to the superiority in weight of the sesamus form 
did not obtain in the instance of Mr. Marshall’s P. sesamus and P. 
natalensis bred 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 natalensis 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 sesamus larva. It should also be borne 
in mind that the larval conditions of the first dry- or wet-season 
brood will probably 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 eet season In Mashona- 
land (Ann. Mag. Nat. Hist., 1901, vol. ii, p. 402), and compare the 
discussion of the succession of cerns phases in Precis by Pro- 
fessor Poulton and Mr. Marshall in Trans. Ent. Soe. Lond., 1902, pp. 
443-449. 
