. L'étude de la vie animale. Zoologie. CH. XIX Influence des habitudes alimentaires et environs 311 forme et la taille de la queue et dans les appendices respiratoires supporté par les jambes ; ils ne sont pas trouvés ensemble, mais vivent dans des piscines de différents degrés de saltness. Maintenant Schmankewitsch ont prélevé des échantillons de ^. salina qui vivent dans l'eau, moins de sel. t'lG. 66.-Taii-Artetnia lobes q[ salina (à gauche) et oi Artemia ntilhatisenii (à droite) ; entre ces quatre étapes dans la transformation de l'une dans l'autre. (À partir de la Chambre. ETtcyclop ; après Schmankewitsch.) sel ajouté progressivement pour le milieu où

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. The study of animal life. Zoology. CH. XIX Influence of Habits and Surroundings 311 shape and size of the tail and in the respiratory appendages borne by the legs ; they are not found together, but live in pools of different degrees of saltness. Now Schmankewitsch took specimens of ^. salina which live in the less salt water, . t'lG. 66.—Taii-lobes q[ Artetnia salina (to the left) and oi Artemia ntilhatisenii (to the right) ; between these four stages in the transformation of the one into the other. (From Chambers's ETtcyclop.; after Schmankewitsch.) added salt gradually to the medium in which they were living, and in the course of generations turned them into A. milhausenii. He also reversed the process by freshening the water little by little. Moreover, he accustomed A. salina to entirely fresh water, and then found that the form had changed towards that of a related genus, Branchipus. This last step has been adversely criticised, but it is allowed that one species of brine-shrimp was changed into another. Many interesting experiments have been made on the effect of chemical reagents on cells, but these are perhaps of most interest to the student of drugs. Still the fact that the form of a cell and its predominant phase of activity may be entirely changed in this way is important, especially when we remember that it was in single cells that life first began, and is now continued. Even Weismann agrees with Spencer's conclusion that " the direct action of the medium was ht.prim.ordializ.cXax of organic evolution." To Claude Bernard, the main problem of evolution seemed to be concerned with variations in nutrition: " L'^volution, c'est I'ensemble constant de ces alternatives de la nutrition; c'est la nutrition consider^e dans sa realite, embrassfe d'un coup d'oeil k travers le temps." John Hunter and others have shown how the walls of the. Please note that these images are extracted from scanned page images that may have been digitally enhance

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