The evolution of man : a popular exposition of the principal points of human ontogeny and phylogeny . already pointed out the remarkable agreementbetween the palingenetic gastrula-forms of animals of themost diverse classes; of Sponges (Fig. 174, A), Polyps,Corals (Fig. 171, I), Medusae, Worms (Fig. 175, B) Star-animals (Echinoderma, 0), Articulated Animals (Arthro-poda, B), Soft-bodied Animals (Mollusca, E), and Verte-brates {F). All these various forms of the palingeneticgastrula are much alike, and are only distinguished by suchunessential and subordinate peculiarities, that the systematicz
The evolution of man : a popular exposition of the principal points of human ontogeny and phylogeny . already pointed out the remarkable agreementbetween the palingenetic gastrula-forms of animals of themost diverse classes; of Sponges (Fig. 174, A), Polyps,Corals (Fig. 171, I), Medusae, Worms (Fig. 175, B) Star-animals (Echinoderma, 0), Articulated Animals (Arthro-poda, B), Soft-bodied Animals (Mollusca, E), and Verte-brates {F). All these various forms of the palingeneticgastrula are much alike, and are only distinguished by suchunessential and subordinate peculiarities, that the systematiczoologist, in his natural system, could only represent themas different species of a single genus. The various kenoge-netic gastrula-forms which have been described were alsoreferable to that original palingenetic form (vol. i. p. 231). Thegastrula proved to be a germ-form common to all classes of DEVELOPMENT OF THE GASTK^A. 65 animals, with the exception of the Protozoa. This highlyimportant fact justifies the inference in accordance with thefundamental law of Biogeny, that the various ancestral. Fig. 174 Fig. 179. Fig. 174.—(^4) Gastrula of a Zoophyte (Gastrophysema), Haeckel. Fig. 175.—(B) Gastrula of a Worm (Arrow-womi, Sagitta). Af ter Kowa-levsky. Fig. 176.— (0) Gastrula of an Echiiioderm (Star-fish, Uraster). AfterAlexander Agassiz. Fig. 177.—(D) Gastrula of an Arthropod (Primitive Crab, Nauplius). Fig. 178.—(E) Gastrula of a Mollusc (Pond-snail, Limnceus). AfterKarl Rabl. Fig. 179.—(F) Gastrula of a Vertebrate (Lancelet, Amphioxtis) AfterKo wale v sky. 66 THE EVOLUTION OF MAN. lines of all these classes of animals have developed phylo-genetically from the same parent-form. This most signifi-cant primaeval parent-form is the Gastraea. The Gastrea was at any rate already present in thesea during the Laurentian period, and by means of itsvibratory fringe hurried about in the water, just like theyet extant free-moving ciliated gastrulae of this age. Pro-bably the
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