Identifier: theoryofevolutio00fran (find matches)
Title: The theory of evolution in the light of facts
Year: 1913 (1910s)
Authors: Frank, Karl, 1875-1950 Wasmann, P. E. Ant and termite guests
Subjects: Evolution
Publisher: London: Kegan Paul, Trench, Trubner & co., St. Louis: B. Herder
Contributing Library: Boston College Libraries
Digitizing Sponsor: Boston Library Consortium Member Libraries

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n differ from the earher one. The more triflingit is, the less also will the embryogeny be altered.Furthermore, there are visible the alterations, in thosegerm stages in which the organs commence to form,which are specially designed for service under the 204 THE THEOEY OF EVOLUTION new life conditions ; ^ for the rest the germ developmentwill proceed as hitherto. If now this unaltered re-mainder is so constituted that there can be clearlyperceived in it a mode of evolution peculiar to a deter-mined type, then we must regard the animal concernedas a member, as a variation of that type. By what causes the deviations inthe completely formedcondition and in theembryonic stages lead-ing thereto are inducedcan then under somecircumstances bedirectly seen. If thelarva, for instance,attaches itself firmlyand at once commencesthe transformationwhich strikes us in theperfect animal, thenwas this transforma-tion formerly causedfor the first time by transfer of the animal to a sessilemode of Hfe.
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Fig. 39.—Barnacle in its forms ofDevelopment. ^ With regard to the time in which the separate tissues and organsbecame differentiated during the embryonic development, there are oftengreat differences in the separate groups of animals. Biologists definetwo great groups, the mosaic and the regulation ova, according to the earlieror later commencement of the differentiation and the therewith connectedgreater or lesser facility of the regulation (restitution) in the embryosproduced from the eggs. EMBKYOGENY 205 (a) A few examples will make this more compre-hensible. On driftwood and sunken piles there is oftenfound a mussel-like animal attached by a stalk—the Barnacle (Lepas anatifera, L.) (Fig. 39). Formerlythey were regarded as mussels, although even on asuperficial examination much is perceived which isnot exactly mussel-like, as for instance the possessionof numerous movable limbs, the clasping feet (Ran-henfilsze). The most remarkable thing is that from the eggsof this animal cr

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