The evolution theory . cu-lus, also perforates the hardwinter buds of the oak, whilethe summer form ,/Syx( th egadei ?albipes, lays its eggs in thetender young leaves of thesame tree. The ovipositor ofthe former is thin and long,that of the latter short andstrong (Fig. 126, A and B),and corresponding also tothe depth at which the eggmust be sunk, or, so to speak, sown in the tissue of the plant, the egg of the summer generationdiffers from that of the winter generation by having a muchshorter stalk (Fig. 126, ei). These little wasps thus afford a beautifulexample of the way in which even marke
The evolution theory . cu-lus, also perforates the hardwinter buds of the oak, whilethe summer form ,/Syx( th egadei ?albipes, lays its eggs in thetender young leaves of thesame tree. The ovipositor ofthe former is thin and long,that of the latter short andstrong (Fig. 126, A and B),and corresponding also tothe depth at which the eggmust be sunk, or, so to speak, sown in the tissue of the plant, the egg of the summer generationdiffers from that of the winter generation by having a muchshorter stalk (Fig. 126, ei). These little wasps thus afford a beautifulexample of the way in which even marked changes in the condi-tions of life of a generation may be associated with transformationsin bodily structure, and we understand how it was possible thatby means of processes of selection the generations which alternateperiodically in the year should come to diverge very considerablyin structure. The example may also serve to illustrate how diverseare the harmonious co-adaptations which such transformations B Fig. 126. Ovipositor and ovum of the twogenerations of the same species of Gall-wasp. A, those of the winter form, Neuroterus heviusculus. B, those of the summer-form, tSpathegaster , ovipositor, ei, ovum. Similarly Adler. 248 THE EVOLUTION THEORY and how necessary, therefore, the continual re-combination of theids of the germ-plasm by means of amphimixis must be. Weunderstand why bi-sexual reproduction was only abandoned inone generation, and that the one in which parthenogenesis was ofconsiderable advantage. But such transformations must have comeabout with extreme slowness, since they were the result of climaticchanges which only come about very gradually. We thus comeagain to the same conclusion to which we were led by our studyof vestigial organs in Man, that numerous species which appear-to be at a standstill are continually working towards their ownimprovement. But for this amphimixis is essential; consequentlythe descendants whi
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Keywords: ., bookauthorthomsonj, bookcentury1900, bookdecade1900, bookyear1904
