290 MKIUSTIC VARIATION. [PART i. 



upper anil lower -uriace> of the same wing, in the several eye-spot.- 

 aloiiM- the margin of th'- -aim- wing, or in all of these, as the case 

 niav 1)'-. 'I'll'' evidence \\ill >hew that there is sometimes a close 

 correspondence between the variations of eye-spots in these several 

 positions. 



Hi it tin nigh these are the matters with which we have now 

 tin' in.. iv din-ct concern it will be convenient to speak at the same 

 time more generally of eye-spots. It should be remembered first 

 that there are eye-spots of various complexity. In the simplesl 

 all the band*, are circular, having one centre; the ocellus is then 

 ml.. complete in one cell of the wing, though sometimes tin 

 outer /ours of colour overspread parts of the adjacent cells. In 

 some cases th.- spot is double, having two centres, the bands being 

 di>pos,-d round them in an hour-glass shape. As to the visible 

 structure of e\v | i..ts it can be seen with the microscope that the 

 colour of the eye-spot lies in the colours of the scales. The scales an 

 arranged in parallel rows running (with little crossing or anasto- 

 mosing) as 1 1< 'arly as possible at right angles to the nearest nervures, 

 being disposed in regard to them much as the circular threads of a 

 cobweb are in regard to the radial threads. Across these rows of 

 scales run the colour-zones, in no way limited or guided by them. 

 On the other hand it can be seen that the patterns are almost 

 wholly made up by the colours of single scales, each having its 

 n\\n colour, particoloured scales being exceptional. The effect 

 thus seen is very like that of a mosaic picture made of similar 

 pieces, or of a design worked in cross-stitch on canvas, all the 

 stitches being in rows and each stitch having its own colour. 



As regards the position of eye-spots it should be noticed that 

 the simpler sort, e.g. those of Morpho or of Satyridoe, are usual/;/ 

 jilni',',1 /// xin-li <i iinxitinn flint eni'li if their centres is on the line of 

 one of the creases or fnlfl-murlcn of the winy, and it sometimes 

 happens th: it these creases seem to begin from the centre of an 

 ocellus. 1-Yoin the fact that the creases for the most part run 

 e\. nlv between two nervures, bisecting a cell, it commonly results 

 that the centre of the eye-spot is exactly halfway between two 

 n.Tvures. The large spots on the hind wings of some Pieridas, e.g. 

 Parnassius <i/i<iflo, are an exception to this rule. 



In that cell of the hind wing which lies between the submedian 

 and first median nervures in many ocellated forms (Satyrida?, 

 Mnrftlio, &c.) there are two creases, and it is especially interesting to 

 notice that in this cell there are commonly two ocelli, one on each 

 civase; but if there is only one ocellus its centre does not corre- 

 spond with the middle of the cell but is nearer to the first median 

 nervuiv, being placed exactly on the anterior of the two creases. 

 In spite of the excessive variability of ocelli, in for instance Satyr- 

 id;e, it appears that they are not formed in situations other than 

 these, being so far as I have seen always on one of the creases '. 

 1 These remarks refer to simple ocelli with one or more definite centres. 



