FUNDAMENTAL RELATIONS OF ANIMALS 117 



their structural complications lean towards other combinations fully 

 realized in a later period, while synthetic types are those which com- 

 bine 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, while Pterodactyles 

 have more the character of prophetic types; so are also Echinocrinus 

 with reference to Echini, Pentremites with reference to Asterioids, 

 and Pentacrinus with reference to Comatula. Full illustrations of 

 these different cases will yet be needed to render obvious the im- 

 portance of such comparisons, and I shall not fail to present ample 

 details upon this subject in my Contributions to the Natural History 

 of the United States. Enough, however, has already been said to show 

 that the character of these relations among animals of past ages, com- 

 pared with those of later periods or of the present day, exhibits more 

 strikingly than any other feature of the animal kingdom the thought- 

 ful connection which unites all living beings through all ages into 

 one great system, intimately linked together from beginning to end. 



SECTION XXVII 



PARALLELISM 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 corresponding to the perma- 

 nent constitution of the lower classes. These suppositions, the results 

 of incomplete investigations, have even become the foundation 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 



^"Lamarck, Philosophie zoologique; Maillet (Pseudon. Telliamed), EJitretiens d'un 

 philosophe hidien avec un inissionnaire frangais sur la diminution de la mer, la 

 formation de la terre, I'origine de I'homme ... (2 vols., Amsterdam, 1748); Oken, 

 Lehrbuch der Naturphilosophie; The Vestiges of the Natural History of Creation 

 (London, 1844). 



