200 Dr. F. A. Dixey 07i 



the whole of our knowledge in this particular. In view of 

 the great difference between the temperate and tropical 

 seasons, it was natural to suppose that the seasonal forms 

 of tropical butterflies would be found to stand in relation 

 to quite other meteorological conditions than those re- 

 sponded to by the Nearctic and Palaearctic species which 

 had previously formed the subject of experiment. So far 

 as I am aware, the only factor found generally operative 

 in these latter cases is a raising or lowering of the 

 temperature ; the direct effect of humidity has been tried, 

 but almost always with negative results. Mr. Marshall, 

 on the other hand, has successfully used heat in combi- 

 nation with both moisture and dryness, and has also 

 employed moisture unaccompanied by heat. By all these 

 means, as will be seen, he has secured results analogous 

 indeed with those of the European observers, but as a 

 rule far less complete. It is possible that there may still 

 be discovered some factor or combination of factors which 

 will produce, in dimorphic tropical species, equally strik- 

 ing results with those to which Merrifield and Standfuss 

 have now accustomed us. Most, however, of the species 

 so far investigated by Mr. Marshall have proved compara- 

 tively resistent to this kind of treatment, and he has no 

 instance of artificial modificcition which can be ranked 

 with the Araschnia levana of many exjjerimenters, or the 

 Selenia tctralunaria of Mr. Merrifield. 



Mr. Marshall's initials are here appended to each separate 

 extract from his correspf)ndence. 



'' Estcourt, Natal ; Dec. 14, 1896. — I only succeeded in 

 getting three eggs of Teracoins toplia* of which I send 

 you one of the resulting specimen^, which is undoubtedly 

 T. auxo, being of the early wet-season form with the upper 

 side black markings not yet fully developed. The eggs were 

 laid within five minutes of one another, and they hatched 

 simultaneously, but one larva pupated a day later than the 

 other two and emerged a day later. The first two examples 



* The result of tliis experiment was communicated by Mr. Mar.shall 

 to the '• Entomologist's Monthly Magazine," 1897, p. 52, and is 

 referred to by Mr. I'rimen in liis address above quoted (Proc. Ent. 

 Soc. Lond., 1S98, p. Ix.xii). It should be noted tliat the name 

 T. topha, Wallgrn., which is now used by both Mr. Marshall and 

 Mr. Trimen to designate the dry-season "^form of T. auxo, is con- 

 sidered V)y Dr. Butler to be applicable rather to an intermediate 

 form between T. auxo and T. keiskamma, Trim., tlie latter being the 

 true dry-season phase. (Ann. Mag. Nat. Hist., 1897, ii, p. 453.) 



