<:i90 DR. J. C. MOTTRAM ON 



will be protected from enemies by mimicking its snrronnflings, 

 and within the ring defined by FGH and El J by means of pro- 

 tective pattern-blending. The relative importance of these two 

 methods of concealment will be according to the likelihood of 

 enemies finding their way into the two areas, and the chance 

 will be as the I'elative size of the two areas : the central area 

 will, however, be at a somewhat greater disadvantage, because 

 the enemy in arriving there, must pass through the outer area, 

 and in so doing may discover its f)i"ey before reaching the centre. 

 The relative importance will also depend upon the eyesight of the 

 enemy and the distance at which it commonly looks for its prey ; 

 those who have watched birds feeding upon insects have often 

 remarked the long distances at which they can see their quarry. 

 In order to illustrate the distance at which the patterns of 

 insects blend, measurements were made in the case of sixteen 

 insects, as shown in the following table. 



It is obvious that the size of an animal must affect the size of 

 its pattern : for instance, a pattern which blends at a, few feet 

 would be useless to an animal the size of the zebra,. It appears, 

 therefore, that it is necessary, whilst giving the blending distance 

 of a pattern, to also state the size of the animal, and the relation 

 of these two in the form of a ratio as is done in the table. 

 Whether by comparing these pattern-blending ratios or indices, 

 it is possible to sepai^ate animals presenting conspicuous patterns 

 from those presenting inconspicuous ones, is beyond the scope of 

 tliis paper. In the case of the insects examined, in some cases 

 the dorsal surfaces of the wings have a high index, whereas the 

 ventral aspects of the lower wings have all low indices, with the 

 exception of the Queen of Spain Fritillary {A. lathonia). In 

 this insect the high figure is probably due to the reflection of t]ie 

 candle-light from the " mirror " spots on the wing. , It has been 

 noted that the larger the pattern, the more effective the outline 

 blending ; on the other hand, the greater the blending distance of 

 the pattern, probably the more conspicuous the animal : other 

 things being equal, it follows, therefoi-e, that a pattern may be so 

 adjusted that the danger of it, shoi't of blending, is counter- 

 balanced by its concealing powers after blending. Finally, 

 attention must be directed to one other aspect of these experi- 

 ments. Deductions have been drawn from experiments carried 

 out with the human eye : thus it is entirely a matter of opinion 

 whether they would a.pply in the case of the eyes of animals. 

 It is known that many animals are short-sighted compared with 

 man, for instance, those of short stature and which for this 

 reason have a near horizon : it may be that the lion at night 

 cannot see the zebra's stripes until \yithin close range. On the 

 other hand, there is some evidence that in the case of certain 

 birds, such as falcons, vision is more piercing than in man. 



However, these deductions from experiments with the human 

 eye are ill.usti-ated in the markings of animals' coats. 



