THE DECADENCE OF BRITISH LEPIDOPTERA. 55 



It is well known that the most universal colours of the more 

 lowly organized moths are the drab-grey and yellow-drab tints ; 

 and this is what one would expect according to my hypothesis, 

 for these are the colours that are derived from the haemolymphs 

 by mere exposure to the aii'. Ths brilliant yellows, reds, &c., 

 are the result of more or less complex chemical processes, which 

 have been slowly effected, probably through the agency of natural 

 selection. 



In connection with the phenomena of pigmentation it is 

 interesting to note that while uric acid may easily be demon- 

 strated by the murexide test in the fluids of the alimentary tract 

 of the pupce of the Saturnidte, it is never present in the hpemo- 

 lymph of the imago ; nor can I detect it in the drab-coloured 

 pigment of the outer edges of the wings. The amount of uric 

 acid in the fluids of the alimentary tract of the pupa increases as 

 the pupa becomes older, so that the fluid which is voided upon 

 emergence is always strongly impregnated with it. In the case 

 of Pieris rapre there is no uric acid either in the alimentary tract 

 or haemolymph of the larva, but it is present in the alimentarij 

 tract of the pupa. It seems to me probable that the uric acid of 

 the alimentary tract of the pupa may be a product of the meta- 

 bolism of the htemolymph that is removed from the fluids of the 

 body by the Malpighian tubules. 



THE PROBABLE CAUSES OF THE DECADENCE OF 

 BRITISH RHOPALOCERA. 



By W. Harcouet-Bath. 



At the meeting of the Entomological Society of London 

 when this subject was brought forward for discussion, judging 

 from the report which is published in the ' Proceedings,' one 

 cannot avoid being considerably struck with the almost total 

 absence of any suggestions advanced by the speakers from a 

 purely evolutionary point of view. One must, therefore, accord- 

 ingly draw the conclusion that the principles and theories 

 propounded by that great naturalist the late Charles Darwin, 

 and his able successor Dr. Alfred Piussel Wallace, have not 

 succeeded in obtaining many adherents among the Fellows of 

 the learned Society under consideration. The chief factors in 

 deciding the decadence of British lUiopalocera, which the 

 majority of those who spoke at the meeting seemed to consider, 

 were adverse climatic influences, and no suggestions or hints 

 were thrown out whatever in support of the hypothesis of the 

 organic environment possessing a preponderating influence in 

 the determination. 



