562 



SCIENCE. 



LVoL. VIII, No. 202 



tion to the animal acquiring them ; and, after the 

 birds have once learned that such and such insects 

 are inedible, any insect, whether inedible or not, 

 that gets itself mistaken for one of the inedible 

 species, will enjoy a similar immunity from at- 

 tack. This device is current in nature, and is 

 termed ' animal mimicry.' Dr. Wallace showed 

 many striking examples of this, — a moth closely 

 resembling in form and marking a powerful wasp, 

 or a wasp imitating an inedible beetle, and a host 

 of edible butterflies and caterpillars imitating to a 

 nicety quite different sijecies that are inedible. 

 A superficial observer would readily mistake one 

 for the other, but the entomologist finds them 

 structurally distinct in almost every particular. 

 In fact, a South American species brightly marked 

 and striped is really our common white cabbage 

 butterfly transformed for purposes of mimicry. 

 The crucial test of all such mimicry lies in the 

 fact that invariably the mimicking and mim- 

 icked species inhabit identically the same territory, 

 and are frequently found together. An excellent 

 illuptration of this was given. Two different 

 authors had written up the descriptions, the one 

 of hard-shell, the other of soft-s^ell beetles of a 

 southern climate ; and Dr. Wallace selected from 

 one volume many cases mimicking the forms 

 pictured in the other volume, and invariably 

 found, on referring to the text, that the two 

 species occupied the same area. 



A curious and for a long time a very puzzling 

 series of facts was that many inedible species 

 imitated one another. The utihty of this is not 

 very evident, and, when the number of examples 

 of it was small, it was regarded as accidental. 

 The explanation has been given by the distin- 

 guished naturalist Fritz Mtiller. It is this : a cer- 

 tain number of the inedible butterflies must be 

 sacrificed in order to teach the young birds that 

 they are inedible. The young bird must experi- 

 ment, try two or three of them, and then will 

 reason from that sample to the whole class. Now, 

 if two inedible species are closely alike, the bird 

 will only have to use up two or three of both 

 species, instead of two or three of each species, 

 before learning that they must be let alone. And 

 thus by clubbing together, the butterflies mutually 

 protect one another against these experimental in- 

 roads. This is not an insigniOcant advantage 

 when the number of birds is large, and, especially 

 if the two species are unequal in the number of 

 individuals they possess, the smaller species de- 

 rives a great advantage. Examples of butterflies 

 maimed by the bills of birds were shown. 



In reptiles we find poisonous snakes imitated 

 by harmless ones ; and in birds the phenomena of 

 sexual coloring are especially marked. Whenever 



the coloring of the two sexes differs, the female is 

 dull, and the male bright ; and this for the reason 

 that the female is more open to attack, especially 

 when taking care of the young and at other 

 times. But when the nest is built in the hollow 

 of a tree or in other not exposed places, it is 

 found that the male and female are equally 

 brightly colored. So, also, in some butterflies the 

 female alone imitates an inedible species. 



The last lecture was devoted to the considera- 

 tion of color in the vegetable world. Here color 

 is not so generally related to the economy of the 

 organism, but is much more the normal product 

 of chemical action. The chlorophyl of vegetable 

 green forms one of the normal characteristics of 

 plant-life. Protective coloring is also not usual. 

 A small plant of the African desert very closely 

 imitates the pebbles among which it takes root. 

 Another African plant has tubers that might pass 

 for small stones. 



Many cases of apparent plant mimicry have been 

 shown to be the result of similar conditions of ex- 

 istence ; as, for example, the strong resemblances 

 of many alpine as well as of marine plants to one 

 another. But a few cases of true mimicry exist. 

 There is a rare non-poisonous fungus which imi- 

 tates a common poisonous fungus, and is always 

 found along with the common species. There are 

 instances, too, of higher plants imitating an 

 orchis that grows in its vicinity ; but these are 

 rare. 



When w^e consider fruits (in the botanical sense) 

 in detail, the phenomena of color become highly 

 important. These colors are largely for the pur- 

 pose of attracting the visits of insects and other 

 animals ; the ulterior object being tlie dissemina- 

 tion of the seeds. The main agencies by which 

 this is effected are mechanical ones, — the wind, 

 and by the visits of aniinals. A few general facts 

 of color are at once explained by this view. Un- 

 ripe fruit is of a protective green color, and where 

 it is disseminated by mechanical agencies along 

 the ground, as in nuts, it takes on a dull brown 

 color. Nuts are protected by hard shells, some- 

 times also by bitter or by prickly surfaces, 

 and show very clearly that the seed within, though 

 edible, was not meant to be eaten. Being suffi- 

 ciently protected otherwise, it has not acquired 

 the property of inedibility. On the other hand, 

 what we popularly know as fruits are intended to 

 be eaten : they are made attractive by a bright 

 and juicy pulp, and the seeds are generally small 

 and smooth, so as easily to be swallowed entire, 

 and to pass through the body of the animal ready 

 for fertilization. The seeds, too, may be bitter, or 

 protected by a parchment-like covering, as in the 

 crab-apple. We see, then, that fruits when 



