24 PKOCEKDIXGS OF THE 



QMie objectioTi may be raised that ilie variation is larpje ami not 

 small — a matter ot' opinion wliicli might be discussed indefinitely. 

 It is siiflicicnt for tlie pi-esent purpose to say that the fusion of 

 certain spots in a pattern, or a slight change of tint over ])art 

 of the surface of a wing are good examples of tlie kind of varia- 

 tion by which mimetic resemblance has been, in my opinion, 

 jierfected. 



b. Jlereditary Transmission of Small Variations in the British 

 Moth Spilosoma mendica. — I owe the two following examples of 

 the hereditary transmission of a very small variation to Mr. A. 

 Bacot, who has kindly presented the material, exhibited to the 

 meeting, to the Hope Department, where it can be studied at anj' 

 time. Concerning S. mendica Mr. Bacot wrote: — " I captured, 

 at Chigwell in 1890, a female specimen of Spilosoma mendica 

 Avhich had a small duplication of two of the black dots situated 

 near the hind margin of the fore wings on tbe upper surface, and 

 also a small spot within the cell near the base of the fore wing. 

 From ova laid by this moth I reared 8 males and 8 females. One 

 male sliows tbe two additional spots near the margin of tlie wing 

 and also the basal spot ; a second male shows, of these markings, 

 only one additional marginal spot, a third male only the basal 

 spot." JS^early all these markings are smaller than in the parent, 

 but all can be distinctly made out wath a lens. 



c. Hereditary Transmission of Smcdl Variations in the European 

 Moth Syntomis phegea. — Tbe second example, referred to by 

 Mr. Bacot in the follow ing paragraph, is even more striking : — 



" In a brood of Syntomis phegea * that I passed on to you there 

 was an example that had a small but very distinct addition to one 

 of the trans])arent spots (I think on one side only). I bred from 

 this example, and some of tbe specimens in the resultant brood 

 showed a similar alteration in the spot. I think that you will 

 have no difficulty in finding the point if you refer to the brood." 



The material of the experiment was deriv'ed from two males 

 and two females bred in 1S99 from Swiss larvte. From a pair of 

 these was reared in 1900 a family of 17 males and 23 females. 

 The central spot of tbe fore wing, — the only one in the cell — 

 which exhibited slight variability in the four 1899 specimens, 

 shows a much wider range in the 1900 family. The differences 

 in size are very marked, in fact in one of the females the spots 

 are evanescent. Even more striking is the extent of the uni- 

 lateral variations, reaching its climax in one male with a semi- 

 circular invasion of the black ground-colour obliterating about a 

 (piarter of the left-hand spot, while the right one retains the 

 normal size and unbroken squarish outline. Considerable but 

 less marked variations of the same kind are present on the left 



* Exhibited, excejit tlio 1902 family, by Mr. I3arot at tlie City of London 

 Kntoniological and Natural tfistorv Society, Feb. 1".', IDOl. Traiisuciioiiti, 

 I'JUl, i>t. xi. pp. 8, 23 (Tille only). 



