General principles of zoology . tage of the axial skeleton: (i) notochord, (2) notochordand vertebral column, the latter at first formed of carti-lage, then of bone. We have here spoken of a parallelism between thefacts of Comparative Anatomy and those of as a matter of fact we should expect a threefold paral-lelism ; for according to the descent theory the system-atic arrangement of animals is conditioned by a third o factor—the historical development of the animal world, orPhylogeny. The boundary stones of phylogenesis, thefossils, must now, so we should expect, in the success
General principles of zoology . tage of the axial skeleton: (i) notochord, (2) notochordand vertebral column, the latter at first formed of carti-lage, then of bone. We have here spoken of a parallelism between thefacts of Comparative Anatomy and those of as a matter of fact we should expect a threefold paral-lelism ; for according to the descent theory the system-atic arrangement of animals is conditioned by a third o factor—the historical development of the animal world, orPhylogeny. The boundary stones of phylogenesis, thefossils, must now, so we should expect, in the successivegeological strata give the same progressive series as thestages of forms found by Comparative Anatomy and Em-bryology. In point of fact we know instances of suchthreefold parallelisms. Comparative Anatomy teaches thatthe lowest developed form of a fishs tail is the diphy- 48 GENERAL PRINCIPLES OF ZOOLOGY. cereal (Fig. 10, A); that from this the heterocercal (J3), andfrom the heterocercal the homocercal form of tail-fin can.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
