General physiology; an outline of the science of life . thorns. In the course of about 15 or 20 minutes the cellsassume the very characteristic shape of Amceba radiosa (Fig. 66, e,f),which is known by the systematists as a very well-definedspecies; they remain in this condition and show the very sluggishmovements of this species so long as the alkalinity of the mediumcontinues. If they are put again into their accustomed water,their shape changes gradually to the usual Umax-form. Manymoulds, which can be accustomed to concentrated salt-solutionswhen these contain sufficient food-stuffs for Muc
General physiology; an outline of the science of life . thorns. In the course of about 15 or 20 minutes the cellsassume the very characteristic shape of Amceba radiosa (Fig. 66, e,f),which is known by the systematists as a very well-definedspecies; they remain in this condition and show the very sluggishmovements of this species so long as the alkalinity of the mediumcontinues. If they are put again into their accustomed water,their shape changes gradually to the usual Umax-form. Manymoulds, which can be accustomed to concentrated salt-solutionswhen these contain sufficient food-stuffs for Mucor, behave hyphae, as a rule, become considerably finer and slenderer thanin the customary water. In many cases, however, changes in thevital conditions affect, not directly the form of the individual, butin a hidden manner the germ-plasm of the sexual cells, so that theoffspring assume forms different from those associated with earlierconditions ; this, however, is rather to be considered under phyleticadaptation. i Cf Verworn (96, 4).. Pig. 65.—A. Branchvpus stag-nalis, fresh-water form ;B. Artemia salina, salt-water form of the samecrustacean. (From Sem-per.) ELEMENTARY VITAL PHENOMENA 185 Fhyletic adaptation, , the gradual adaptation of the series offorms to existing vital conditions, has a disproportionately great,perhaps a determinative, significance in the form-changes ofphvlogenetic development. It takes place in a manner whollydifferent from that of individual adaptation. Darwins immortalwork (59; consists in explaining naturally the surprisingpurposefulness in the organic world by revealing the mode ofphyletic adaptation. According to Darwins theory of selectionthe adaptation of organisms to external conditions takes place, notby the immediate change of the single individual, but by natural ^ a>
Size: 1511px × 1653px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookidgen, booksubjectphysiology
