282 



MERISTIC VARIATION. 



[part I. 



The cases of S. carpini, No. 422, and of Bombyx quercus, No. 

 429, nevertheless suggest that Variation in number of wings is of 

 the same nature as that seen in teeth, digits, or other parts 

 standing in a Meristic Series. In the specimen of S. carpini 

 it is especially noticeable that on the side having three wings, 

 both the wings formed as secondaries were smaller than the 

 secondary of the normal side ; but in other cases, G. rhamni 

 (No. 427) for instance, this was not the case, and the wing 

 standing next to the extra wing was normal. Both these con- 

 ditions are frequently found in cases of the occurrence of super- 

 numerary parts in series: for two members of a varying series 

 may clearly correspond jointly with a single member of the 

 normal series, or on the contrary a new member may stand ad- 

 jacent to members in all respects normal as in G. rhamni (No. 427.) 

 *422. Saturnia carpini $ , having a supernumerary hind wing. The 

 specimen is rather a small female. The right wings and the 

 left anterior wing are normal, but in the place of the left posterior 

 wing, there are two rather small but otherwise nearly normal 

 posterior wings. Of these the anterior is rather the larger and 

 to some extent overlaps the posterior. The costal border of the 

 posterior wing is folded over a little so that its width cannot 

 be exactly measured. 



Right hind- wing normal 

 First left hind-wing 

 Second left hind-wing 



Greatest 

 length. 



22*5 mm. 

 20-5 „ 

 15-5 „ 



Greatest 

 width. 

 19 mm. 

 14 

 11 „ about. 



423 



From the fact that the bases of these two wings are greatly 

 overgrown with hair, it is difficult to distinguish their exact points 

 of origin from the body, but so far as may be seen, the second 

 arises immediately behind and on a level with the first. The 

 neuration of each of the two small wings is identical with that 

 of a normal hind-wing. The scaling is perfect on both surfaces 

 of both wings, but is perhaps a little more sparse on the anterior 

 of the two abnormal ones. In colour the anterior abnormal wing 

 is rather light, but the posterior one is identical with that of 

 the other side. The markings on each of the wings are normal, 

 but are on a reduced scale in proportion to the size of the wings. 

 This is especially remarkable in the case of the ocelli, which are 

 both of a size greatly less than that of the ocellus of the normal 

 hind wing of the right side. 



The two wings were in every respect true left hind-wings 

 and were in no way complementary to each other. [Specimen 

 in collection of and kindly lent by Dr Mason.] 



Bombyx rubi $ : 5th wing on left side. The additional wing 

 was placed behind the left posterior wing. It was of normal 

 structure as regards scaling and coloration. Its length was that 

 of the hind-wing but in breadth it did not exceed 6 mm. The 



