528 Mr. Louis B. Prout on Xanthorhoe ferrugata 



bred from purple x purple, these being brother and sister 

 reared from wild purple female). (2) 37 purple, 9 black, 

 1 intermediate (^ parent purple, from a wild purple 

 female ; $ parent purple, a member of the brood just 

 described as (1) ). (^3) 6 purple, 11 black (^ parent purple, 

 from a wild purple $ ; ^ parent purple, likewise from a 

 wild purple ^). (4) 13 purple, 2 black, 1 intermediate 

 (^ parent purple, from wild purple $ ; $ parent purple, 

 from wild purple ^ X black $ , the latter the offspring of 

 black ^ and $, which, in their turn, sprang from wild 

 purple and wild black ^ respectively). (5) 13 purple, 

 8 black (^ parent purple, from a wild purple ^ ; $ parent 

 purple, likewise from a wild purple $). (6) 16 purple, 

 7 black (^ parent purple, from wild purple ^ ; $ parent 

 purple, from the brood just noticed as No. (3)). These 

 figures give a total for the six broods, of 137 purple, 

 58 black, 2 intermediate; or respectively (omitting 

 fractions) 69 per cent., 29 per cent., 1 per cent. It will 

 be observed that in one case, No. (3), the black form 

 actually preponderated, notwithstanding a known purple 

 ancestry for two generations ; in the other five, the per- 

 centage of black varied from 381 per cent, to 12*5 per 

 cent, approximately. 



It will be at once manifest, that the weakness of the 

 above statistics for the purposes of elucidation of Mendelism 

 consists in the almost constant necessity of introducing 

 wild stock of unknown pedigree. Nevertheless, the 

 "discontinuity" of the two forms and the apparent "purity" 

 of most members of the black race give sufficient im- 

 pression of a "Mendelian species" to justify my offering 

 a few comments. 



I cannot refrain from remarking, in the first place, that 

 if only certain species are " Mendelian " in their behaviour 

 — as seems to be liinted by some writers, e. g. Doncaster 

 in "Ent. Record," xviii, p. 249 — it would, to me, be a grave 

 argument against our attributing the Mendelian pheno- 

 mena, when observed, to any deep-seated biological cause ; 

 it is inconceivable that, among organisms so homogeneous 

 as the various species of Lepidoptera — or even Insecta — 

 there could be cytological differences vast enough to allow 

 of gametic purity in certain cases only. Probably, how- 

 ever, it may be a sufficient reply that all species are really 

 alike " Mendelian " in vital organization, but that it by no 

 means thence follows that a particular manifestation of 



