chap, xii.] EYE-SPOTS. 291 



On looking at such a series of repeated ocelli as those on the hind 

 wing of Pararge megcera, from this fact that the ocelli are on these 

 creases or folds the question naturally arises whether the wing may not 

 have been, in its development, folded along these creases so as to bring 

 the ocelli into contact with each other like the fold-edges of a fan. If 

 this were the case it might be supposed that the repetition of the ocelli 

 was due to the action of some one cause on all the folded edges 

 together. As a matter of fact, however, so far at least as can be 

 judged from the condition of the wings in the pupal state before scales 

 or pigments are excreted, there is no such folding, but each wing is 

 laid smoothly out, and the increase in extent of the wings of the imago 

 is attained, not by a process of unfolding, but by a stretching of the 

 elastic wing-membranes on inflation from the trachea?. On the whole 

 it does not seem likely that the repetition of similar eye-spots on the 

 Lepidopteran wing arises in any way more immediately mechanical 

 than that by which other repeated patterns are elsewhere formed on 

 animals. 



The Variation of eye-spots as already stated may be very great, 

 and examples are to be given both of the total absence of large 

 eye-spots present in the normal, and of the presence of perfect 

 eye-spots in abnormal places. Besides these extreme cases there 

 is immense Variation in the degree to which eye-spots are develop- 

 ed, and such variability is nearly always to be seen in any species 

 possessing simple ringed ocelli. In the manner of Variation of 

 ocelli the following things are noteworthy. 



(1) The whole of an eye-spot, centre and various concentric 

 bands together, may be wanting ; conversely a whole new eye-spot 

 having the centre and all the bands pertaining to the normal eye- 

 spot of the species may suddenly appear upon a crease normally 

 bearing no eye -spot. Eye-spots therefore may come or disappear 

 in their entirety. 



(2) If a number of specimens of some much ocellated species 

 are taken and compared, examples will be found in which some of 

 the normal ocelli are absent altogether. But besides these there 

 may generally be found specimens having an ocellus in a reduced 

 and imperfect condition. Speaking generally such reduction com- 

 monly occurs by diminution of the diameter of the whole spot ; but 

 if any of its component parts are wanting the centre is the first to 

 disappear, then the next innermost band, and so on. In Fig. 76 is 

 shewn a series of specimens illustrating this fact in the case of 

 Hipparchia tithonus. The eye-spot in its least form is represented 

 by a plain black patch. In the more complete condition a white 

 centre appears. A similar case in Morpho is shewn in Fig. 81. 

 Here on the right side a certain eye-spot is absent altogether, 

 while on the left side it is present in a reduced state ; the white 

 centre and the innermost broad black band are absent, and the 

 actual centre is of the yellow-red colour which in the normal eye- 

 spot of the species is the third colour from the centre. The spots 



19—2 



