206 THlfi entomologist's KECOkD. 



found for exiuuple in some greenish-tinted specimens of KaUiiiia, but 

 mainly by certain species of the South American genus Catuni'iihclr, all 

 of which are forest-butterflies, and which, with many species having 

 dark brown under surfaces, present some also with bright green under 

 surfaces — a green that is not like the fresh green of our beech and oak 

 trees, but resembles the bright under surface of the cherry-laurel 

 leaf, and is the colour of the under surfaces of the thick leathery 

 leaves, coloured dark green above, borne by many trees in the tropics." 



The essential difference between the selection process, as explained 

 by Weismann, and the old theory is this : — That under the old con- 

 ception variations were fortuitous, and that selection had to wait for 

 these chance favourable variations before it could commence its work. 

 Under the new conception every portion of the organism contains in 

 its initial stages an indefinite number of variations within itself, some 

 of which are almost sure to be in the direction required. Selection 

 chooses those she requires, and by the process of intra-selection com- 

 pels them, as it were, to overcome their competitors, and utilises them 

 to produce those results which will be of service to the organism. 



" This is the only way," Weismann says, "in which lean see a pos- 

 sibility of explaining the phenomena of mimicry — the imitation of one 

 species by another. The useful variations must be produced in the 

 germ itself by internal selection-processes if this class of facts is to be 

 rendered intelligible. I refer to the mimicry of an exempt species by 

 two or three other species, or, the aping of (liferent exempt patterns by 

 one species in need of protection." 



It has until recently been considered that some degree of similarity 

 between the copy and the imitation was present from the start, but 

 Dr. Dixey has recently shown* that even this is not at all necessary. 

 Weismann considers that the minute similarity in the design which 

 exists between the mimic and the mimicked, would have been 

 impossible if the process of adaptation had depended entirely upon 

 personal (individual) selection. Were this so, a complete scale of the 

 most varied shades of colour must have been continuously presented 

 as variations in every species, which certainly is not the case. 



" For example, when the exempt species Acraea eijina, whose 

 coloration is a brick-red, a colour common only in the genus Acraea, 

 is mimicked by two other butterflies, a Vapilw and a PsewJacraea, so 

 deceptively, that not only the cut of the wings and the pattern of their 

 markings, but also that precise shade of brick-red, which is scarcely 

 ever met with in diurnal butterflies, are produced, assuredly such a 

 result cannot rest on accidental, but must be the outcome of a 

 definitely directed, variation, produced by utility. We cannot assume 

 that such a coloration has appeared as an accidental variation in just 

 and in only these two species, which fly together with the Acraea in 

 the same localities of the same country, and the same part of the 

 world — the Gold Coast of Africa. It is conceivable, indeed, that non- 

 directed variation should have accidentally produced this brick-red in 

 a muile case, but that it should have done so three times and in three 

 species which live together, but are otherwise not related, is a far more 

 violent and improbable assumption than that of a casual connection of 

 this coincidence. Now, hundreds of cases of such mimicry exist in 

 which the colour-tints of the copy are met with again in more or less 



* "On the relation of mimetic patterns to the original." — Trans. Ent. Soc. 

 Lond., 1896, pp. 65-81. 



