CHAP, xii.] EYE-SPOTS. 293 



loss of the spot standing at one of the ends of the series. This is 

 easily seen in P. megcera, &c. Likewise as was found in Teeth, 

 disappearance of such a terminal eye-spot is associated with 

 reduction in the size of the other members of the series, and 

 especially of those nearest to the place of the absent member. 

 If as in Satyrus hyp&ranthus and many others, the series is broken 

 into groups, then as in the case of heterodont dentitions containing 

 gaps, a new member may be added on to the end of either group. 



(4) The condition of the ocelli may vary similarly arid simul- 

 taneously in both anterior and posterior wings. In a series of 

 Saturnia carpini for example I notice that the size of the ocelli 

 varies greatly, those of a particular female specimen in the Cam- 

 bridge University Museum being nearly a quarter larger than those 

 of the specimen having the smallest ocelli ; but the size of the 

 ocelli in the hind wings of each individual varies with that of 

 the ocelli in the fore wings not less closely than the size of the 

 right ocelli does with that of the left. 



(5) This correlation between the wings of the two pairs is seen 

 also in the presence or absence of ocelli as exhibited for instance 

 in H. tithonus (Fig. 76). It is of course often very irregular, but 

 for our purpose it is even of consequence that such correlation 

 may occur sometimes. 



(6) As mentioned, ocelli are often coincident on the upper and 

 lower surfaces. When this is so, the degree of development of the 

 spots on the one surface is generally an accurate measure of the 

 degree to which they are developed on the other surface. But in 

 species having spots developed thus coincidently on the two sur- 

 faces it can be found that, in varying, an ocellus always first 

 appears in its least condition either on one surface or on the other, 

 and not indefinitely sometimes on one and sometimes on the 

 other. In P. meycera, for example, ocelli of both pairs of wings 

 can be seen on the under surface when not formed on the 

 upper and conversely. Nevertheless there is always a close corre- 

 lation between the degrees of development on the two surfaces. 



(7) Lastly, attention is called to the circumstance that in two 

 cases of great variation in ocellar markings there was a variation 

 in the neuration. In the first case, P. megcera, No. 458, the second 

 median nervure was absent from both fore and hind wings. In 

 the fore wing upon the line where it should be there was an eye-spot: 

 in the hind wing the eye-spots of the two cells which should be 

 separated by the second median were partially coalescent. In the 

 other case, S. carpini, No. 459, the large ocellus was absent from 

 each wing, and it is stated that a nervure was also absent, but of 

 this case no proper description has appeared, and it is uncertain 

 which nervure was absent. When however these facts are con- 

 sidered in connexion with the circumstance that ocelli stand on 

 the creases of the wings it seems likely that in some way unknown 

 the positions and perhaps even the existence of the eye-spots may 



