118 ESSAY ON CLASSIFICATION. Part I. 



or necessary reference to either embryonic development or succession in time, as the 

 Chambered Cephalopods. Such types I call ^;ro^rc.s57>e ti/pes} 



Again, a distinction ought to be made between prophetic types proper and 

 Avhat I Avould call si/nthetic ti/pes, though both are more or less blended in nature. 

 Prophetic types proper, are those which in their structural complications lean towards 

 other combinations fully realized in a later period, wdiile synthetic types, are those 

 which combine, in a well balanced measure, features of several types occurring as 

 distinct, only at a later time. Sauroid Fishes and Ichthyosauri are more distinctly 

 synthetic than prophetic types, wdiile Pterodactyles have more the character of 

 prophetic types ; so are also Echinocrmus with reference to Echini, Pentremites with 

 reference to Asterioids, and Pentaci'inus with reference to Comatula. Full illustra- 

 tions of these different cases will yet be needed to render obvious the importance 

 of such comparisons, and I shall not fail, in the course of this work, to present 

 ample details upon this subject. Enough, however, has already been said to show, 

 that the character of these relations among animals of past ages, compared with those 

 of later periods or of the present day, exhibits more strikingly than any other 

 feature of the animal kingdom, the thoughtful connection which unites all hving 

 beings, through all ages, into one great system, intimately linked together from 

 beginning to end. 



SECTION XXVII. 



PAEALLELISM BETWEEN THE STRUCTURAL GRADATION OF ANIMALS AND THEIR 



EMBRYONIC GROWTH. 



So striking is the resemblance of the young of higher animals to the full-grown 

 individuals of lower types, that it has been assumed by many writers that all the 

 higher animals pass, during the earlier stages of their growth, through phases cor- 

 responding to the permanent constitution of the lower classes. These sujjpositions, 

 the results of incomplete investigations, have even become the fovmdation of a 

 system of philosophy of Nature, which represents all animals as the different degrees 

 of development of a few primitive types.^ These views have been too generally 

 circulated of late, in an anonymous work, entitled "Vestiges of Creation," to require 



^ Agassiz, (L.,) On the Difference between don. Telliamed,) Entretiens d'un Philosophe indien 



Progressive, Embryonic, and Prophetic Types, etc., avec un missionaire fran^ais, Amsterdam, 1748, 2 



Proc. Am. Ass. Adv. Sc, Cambridge, 1849, p. 432. vols. 8vo. — Oken, (Lor.,) Lehrbiich der Natur-Plii- 



^ Lamarck, q. a., p. 26. — DdMaillet, (Pseu- losophie, q. a., p. 18. — The Vestiges of Creation, etc. 



