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Show 1887.] VALUE OF COLOUR AND MARKINGS IN INSECTS. 261 falling therefore under tbe influence of natural selection. Knowing that increasing efficiency in protective measures is counterbalanced by increasing keenness and cunning on the part of enemies, it is easy to see how, as a response to an advance by the latter, a species might take advantage of such an incidental quality to adopt an entirely new line of defence. The concealment of the larvae we are considering is evidently very successful, but if it were seen through far more frequently than at present, and yet the larvse were always rejected with disgust, there would be more and more opportunity and necessity for the enemies to remember the experience; and the further the species varied away from the beaten path of protective colouring, tbe greater aid would it afford to memory, which, although that of another animal, is in this respect of far less importance for the possessor than for the larva itself. I need hardly point out that in speaking of an advance in the keenness of Vertebrate insect-eaters, I mean an advance in the power of detecting all such larvse, so that there would always remain a large proportion of palatable species; while the new line of defence would only be open to such few of them as possess the quality of distastefulness in a marked degree. I am quite aware that there is another possible explanation of the unpleasant qualities in M. typica ; i. e. that they are the remnant of a former defence by such means accompanied by corresponding coloration, &c.; but while this may explain similar facts in the case of certain other species, I do not think that it is likely to hold in the instance of M. typica, for the protective habits and appearance are correlated in so perfect a manner that we are compelled to assume that a very long period of time must have been covered in the attainment of so unusual and specialized a result. It now remains to consider the other exceptions which are of less theoretical importance although of extreme interest. As the same species have occurred before under other tables, it will be well to shortly tabulate the results of all the instances among Lepidoptera in which experiments have been made upon more than one stage (see Table, p. 262). I much hope that future experiments will enable us to extend this Table, but short as it is, it appears to point to several interesting conclusions. In the first place there is no known instance of distasteful qualities in stages later than tbe larva when the latter is itself palatable. This statement will doubtless be true of the great majority of species howevercompletebe the experimental investigation, and it points to the conclusion that this method of defence arose first in the larval stage. Such a relation is to be expected ; for the species is exposed to more danger and is more helpless at this period than at either of the subsequent stages. The unpleasant taste appeals to non-parasitic enemies which devour insects; but the almost complete limitation of the attacks of insect-parasites to the larval stage must bear in an important way upon the other modes of protection in this stage, tending to produce that extraordinary specialization in defensive methods which are well known to occur. The imago can escape by flight, and the pupa, if exposed, may render |