Proceedings of Learned Societies. 301 



Mr. Wallace considered that variation was by no means the simple 

 fact that it has generally been regarded, bnt that it included the 

 several phenomena of simple variability, of the existence of the 

 same species in two or more forms, viz., Dimorphism or Polymor- 

 phism. Also, what may be termed local forms, and the considera- 

 tion of sub-species and true species. 



Simple variability, in which the offspring irregularly and, as it 

 were, accidently differ from their parents, is of the same nature as 

 that so characteristic of domestic animals, 



Polymorphism or dimorphism differs from simple variability in 

 the fact that the variations are more or less constant or regular. 

 Thus, in the Papilio Memnon the males are always uniform both 

 in form and colour, being bluish black. Some of the females re- 

 semble the males in shape, but are ashy-brown in colour. Others 

 have wings with spoon-shaped tails, and marked with white. Either 

 of these females will produce males and females of both forms, but 

 it is remarkable that intermediate forms between these two varieties 

 of females never occur. 



Similar instances of polymorphism among the females occurs in 

 the Papilio pammon and P. ormenus. 



These phenomena of polymorphism may be illustrated by sup- 

 posing an island inhabited by white men, with black, red, and yellow 

 women, and that, even after many generations, the males born were 

 all white, and the females indifferently red, yellow, and black, irre- 

 spective of the colours of their female parents. In many cases the 

 difference between the polymorphic forms of the same animal is so 

 great that they have been described as belonging to distinct species. 



The influence of local causes, such as the presence or absence of 

 particular enemies, tends to produce that remarkable variation 

 known by the term Mimetic Analogy. For example, the batter- 

 flies of a group known as the Danaida} have a peculiar scent, which 

 renders them obnoxious to birds of prey, hence they are free from 

 persecution. 



If, in the course of the accidental variations to which all animals 

 are subject, a Papilio resemble a Danais, even slightly, in form and 

 colour, it will escape persecution more than if it had remained un- 

 changed ; and each succeeding generation, those Papilios most like 

 the Danaidae will be the most protected and the most likely to in- 

 crease in numbers. This process will, therefore, gradually but cer- 

 tainly produce a constantly increasing likeness or mimetic analogy, 

 until at last one insect can hardly be distinguished from the other 

 except by a close examination of the structural peculiarities. 



SOCIETY OF ARTS.— April 13. 



New Method of Preserving Meat. — Dr. J. Morgan read a 

 paper on a new method of preserving meat. According to this 

 mode, the animals to be killed have an opening made in the chest, 

 through which the heart is reached. Incisions aro then made into 

 the arterial and venous sides of this organ, and a stream of water, 

 the force of which is obtained by its flowing from an elevated cis- 



