The doctrine of descent and Darwinism . Amphioxus.^ > L Testacea. Primordial Vertebrata. Annulosa. As we have seen above, the most important indicationsof the pedigree of the species are contained in the evo- PEDIGREE OF VERTEBRATE ANIMALS. 251 iutionary history of the individual. Only, if all verte-brate animals testified their family connection by agree-ing inter sc in the distribution of the germ as well asin the fundamentally important organs, the spinal cordand the vertebral column, this token of their descentfrom inferior animals, which is unconditionally demandedby the theory, seemed
The doctrine of descent and Darwinism . Amphioxus.^ > L Testacea. Primordial Vertebrata. Annulosa. As we have seen above, the most important indicationsof the pedigree of the species are contained in the evo- PEDIGREE OF VERTEBRATE ANIMALS. 251 iutionary history of the individual. Only, if all verte-brate animals testified their family connection by agree-ing inter sc in the distribution of the germ as well asin the fundamentally important organs, the spinal cordand the vertebral column, this token of their descentfrom inferior animals, which is unconditionally demandedby the theory, seemed to be entirely wanting. In otherwords, it seemed that in all vertebrate animals thememory of their original derivation had been obliteratedby curtailed development (comp. p. 211). Thus the caseremained until Kowalewsky a few years ago studied thedevelopment of the lancelet (Amphioxus), the lowestvertebrate animal known, and showed that in this crea-ture the typical phenomena of vertebrate development. Fig. 22. Larva of the Lancelet after Kowalewsky. are preceded by the phases required by the have already made acquaintance with this form ofdevelopment (p. 51, &c.), and we here again point out itsprofound significance. It is only when the Amphioxushas passed through the phase of the vibrating, sac-like 252 THE DOCTRINE OF DESCENT. gastrula larva that the future dorsal side becomes flat-tened, and the protuberances arise, which shortly afterclose into the sheath of the spinal marrow, while under-neath originates this important cellular column, thechorda dorsalis, or notochord. With this the lanceletbecomes a vertebrate animal, and the preceding phasesdo not (according to the view at one time inculcatedby C. E. V. Baer respecting such phenomena) recallthe inferior and undeveloped in general by the ab-sence of differentiation, but they agree in genesis anddistribution, in the differentiation of their cellular layers,and in their totality, with the Gastrula phases of inver
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