i8 9 6. SOME NEW BOOKS. 273 



the group which, in the main, agrees with that put forward by Dr. Dixey 

 some years ago, from a minute comparison of the wing-markings. 

 Comparing the Palaearctic species with those of other regions, he 

 would derive V. atalanta from its Oriental congeners, and the other 

 species from American forms. On the question of the origin of species, 

 Dr. Standfuss is in agreement with Dr. Eimer's theory of develop- 

 ment through external influences. 



It is six years since the issue of the first part of Dr. Eimer's work, 

 dealing with the phylogeny of Papilio podalirius and its related 

 species. This second instalment traces the presumed development 

 of the Papilios of the turnus, machaon, and listerias groups. The modi- 

 fications of a typical wing-pattern presented by a related series of 

 butterflies have before offered a tempting field for evolutionary specu- 

 lation. Here Dr. Eimer brings to our notice a series ranging from the 

 male P. daunas with the broad expanse of its creamy-yellow wings 

 crossed by comparatively narrow black bars, through forms (such as 

 our own P. machaon) in which the black markings are broader and tend 

 to become joined together, on to species like P. asterias and P. troilus, 

 whose wings present a wide expanse of black with the cream colour 

 reduced to a few spots. And it is instructive to find at almost the 

 extreme terms of the series the yellow male of P. turnus and the dark 

 var. glauca of its female. 



These butterflies are used by Dr. Eimer as the text for theorising 

 on some of the burning biological problems of to-day. Those who 

 recall the first part of this work, and his book, a year earlier, on the 

 Origin of Species by the inheritance of acquired characters, will 

 expect him to find in the butterflies arguments against Weismann's 

 views. And they will find that, not Weismann only, but the funda- 

 mental Darwinian position is attacked. We are told again and again 

 that natural selection is powerless to originate species ; it can but 

 preserve species which have already been developed by the action of 

 the physiological laws of growth and modification in organisms, and 

 the influence of environment. Dr. Eimer insists that changes of the 

 markings in butterflies which indicate specific differences cannot be 

 of use to the insects, while they can be initiated by changes in tem- 

 perature or food-supply. He apparently believes that the living 

 species we have now before us are links in the direct line of a 

 development which may proceed by slow degrees or, exceptionally, 

 by sudden jumps. Curiously, he considers that the var. glauca of 

 P. turnus was produced in the latter way. As the action of a changed 

 environment on the physiological forces of the organism induces the 

 production of a new variety or species, so constancy of conditions will 

 fix the new form as a species ; this principle is called "genepistasis." 

 Then the intercrossing of the new stock with the parent form (if 

 their geographical ranges overlap) is prevented by the action of 

 " Kyesamechany " — that is Romanes' principle of physiological 

 selection, though Dr. Eimer claims to have enunciated the idea 

 twelve years earlier than our lamented Oxford naturalist. As might 

 be expected, Dr. Eimer disbelieves in the mimicry theory, and would 

 explain the facts of resemblance by the action of similar conditions 

 producing similar effects in parallel series. It may be doubted if the 

 argument for natural selection is much weakened by Dr. Eimer's 

 considerations. Though a change in the wing-patterns may of itself 

 be of no use to an insect, yet that change may be the necessary 

 accompaniment of some variation in structure or habit of the greatest 

 possible use. 



Geo. H. Carpenter. 



