NATURAL SELECTION 247 



throughout the Lepidoptera makes the application of the 

 selection theory difficult. 



One possible method of acquiring distasteful properties does 

 not involve their hereditary fixation or the action of selection. 

 Eltringham (1910, pp. 1 12-13) has shown that the cryptic 

 larva of a Geometrid moth may be distasteful to lizards after 

 feeding on ivy, though palatable when fed on other plants. 

 It is possible that unpalatability could be acquired in this way 

 without even being hereditarily fixed ; only the instinct to lay 

 eggs on the particular plant would be permanent. 



Direct evidence. — We have assembled in another part of this 

 chapter the evidence so far produced that there is a selective 

 elimination of given types. Some of this evidence relates to 

 differences of colour, surface and modelling, and may be briefly 

 summarised here for our immediate purpose. Ten cases relate 

 to differences of colour, and of these three (Haviland and 

 Pitt, Pearl, Poulton and Saunders) provided no evidence for 

 the occurrence of selection. Five cases (Boettger, Jameson, 

 Davenport, Harrison, and Trueman) are rated as defective in 

 respect of the procedure adopted. For one (Kane) another 

 possible explanation, besides that of selection, is available. 

 In the remaining case (di Cesnola) the procedure is held to 

 be satisfactory and a selective result is discernible ; but, as 

 the animals in question were exposed to only one particular 

 set of external conditions, the analogy with Natural Selection 

 is held to be highly questionable. 



On the whole, then, the direct evidence that a particular 

 type is selected on account of its ' harmonising ' colour must 

 be held to be defective. 



Experimental and other evidences. — Morton Jones (1932) has 

 published a very important study of the relative acceptability 

 of insects to birds — a study in which the novelty of the methods 

 shows how little the possibilities of testing these theories experi- 

 mentally have been exhausted. The start of the experiments was 

 the establishment of ' bird-tables ' on the edge of a piece of 

 natural woodland. These tables were provided with water and 

 food, to which a number of birds (seven species) nesting in the 

 neighbourhood used to resort. During each experiment an 

 average of fifty freshly killed insects was arranged on the tray, 

 watch was kept to record the bird visits made and at intervals 

 the insects remaining were tabulated. A numerical rating of 



