CXXXIV 



"karyokinesis varies but slightly within each species, no matter 

 whether the synpatric specimens crossed are externally 

 similar or dissimilar, and difiers from the number observed 

 in allied species. If, however, two species are crossed, the 

 number of particles is very much lower, while an intermediate 

 number results in the case of the crossing of two geographical 

 races of a species. That is a most interesting confirmation of 

 the conclusion drawn from the morphology of the imagines 

 that geographical races are of a different standing in evolution 

 than individual varieties. 



However, in practice it is not always easy to decide whether 

 a variety is really geographical. We have seen here exhibited 

 more than once a certain class of variety which appears in 

 years with an abnormal season. An excessive and prolonged 

 rainfall or continued drought has a marked influence on the 

 size and colouring of the Lepidoptera. Such wet or dry forms 

 would disappear with the return of the climate to normal 

 conditions. The material in our collections from tropical 

 countries is frequently collected in one season only, or even in a 

 few weeks, and in such circumstances we may easily take the 

 product of an abnormal spell of weather for a geographical 

 variety. The documentation in our collections unfortunately 

 is limited, and therefore the work based on them remains 

 always open to correction. 



I thank you for the attention with which you have listened 

 to this Address. Before leaving the Chair I should like to 

 give expression to my gratitude to the Officers and Council 

 for their untiring assistance extended to me during my term 

 of office, and to the Society for having honoured me by the 

 election as its President. The two years were full of interest- 

 ing experience, and they will always remain as a very pleasant 

 memory. 



