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to a state of extreme wretchedness, the prey of the most filthy and disgusting 

 diseases, divested of a covering, unsheltered, except by caves and dungeons, 

 from the inclemency of the seasons, exposed to all the extremities of want and 

 famine ;" and in the end, as Sir Joseph Banks, speaking on this subject, has 

 well observed, "driven with all the larger animals from the face of the earth." 

 You may smile, perhaps, and think this a highly coloured picture, but you will 

 recollect, I am not stating the mischiefs that insects commonly do, but what 

 they would do, according to all probability, if certain counter- checks, restraining 

 them within due limits had not been put in action ; and which they actually 

 do, as you will see, in particular cases, when those counter-checks are 

 diminished or removed. 



It might, indeed, be supposed, that the injuries which can be inflicted upon 

 man by insects have often been exaggerated, but our own experience dining 

 the last few years completely justifies these ideas. You may, for example, 

 remember the nearly total annihilation of the cabbage, cauliflower, turnip, and 

 other vegetables belonging to the large cruciferse in the year 1862, caused by an 

 aphis which had not previotisly appeared in this country. Our apple trees are the 

 prey of another insect of the same kind — the aphis lanifera — commonly called 

 the American blight, which has put a stop to the cultivation of orchards on a 

 large scale. The rapidity with which these creatures increase is something 

 marvellous, though less so when we find that the ordinary laws of generation 

 are suspended in regard to them, the production of young without fecundation, 

 being common to the whole family. Bonnet long ago demonstrated, by a series 

 of most carefully conducted experiments, that at least five generations of the aphis 

 sambuci may succeed each other, the females never pairing. The oak aphis 

 carried this to the ninth generation, and, strange to state, he found that 

 whilst, after pairing, the aphides produced ova, in other cases they produced 

 their young alive. Reaumur computes that each aphis may produce about 

 ninety young, and that in consequence, in five generations the descendants from 

 a single insect would amount to the astonishing number of 5,904,900,000. 

 " Were it not," says Mr. Swainson, "that these immense multitudes are called 

 into being to furnish food for other races, they would be sufficient to destroy 

 vegetation and annihilate the empire of Flora." 



Having thus (I am afraid, however, in a very off-hand manner) pointed 

 out to you the leading characteristics and distribution of the Flora and Fauna 

 of these islands, I will now call your attention to what has aptly been termed 

 the " Struggle for Existence " which living organisms of all kinds, are exposed 

 to in a state of nature, and point out in what manner variation lends its aid in 

 protecting both animals and plants from extinction under that struggle. In 

 doing this I shall not hesitate to borrow largely from Mr. Dai-win's work. 

 After adverting to the acknowledged variability of organic beings in a state of 

 nature (to which I have called your attention in an earlier part of this lecture) 

 he asks, " How all those exquisite adaptations of one part of the organization 

 to another part, and to the conditions of life, and of one distinct organic being 

 to another, have been perfected ] How it is that varieties, (which by the way, he 

 has called ' incipient species '), became ultimately converted into good and 

 distinct species, which, in most cases, obviously differ from each other far more 

 than do the varieties of the same species 1 How those groups of species which 

 constitute what are called distinct genera, and which differ from each other 

 more than do the species of the same genus, have arisen 1" And he proceeds 

 to answer these questions by saying, that the results referred to all follow from 

 the "Struggle for Life," in which all the members of the organic world are engaged. 

 " Owing to this struggle," he observes, "any variation, however slight, and 

 from whatever cause proceeding, if it be in any degree profitable to an 

 individual of any species, in its infinitely complex relations to other organic 



