FUNDAMENTAL RELATIONS OF ANIMALS 119 



ology of Crustacea. I have further shown that the young of Ma- 

 croura represents even Entomostraca forms, some of these young 

 having been described as representatives of that order. The corre- 

 spondence between the gxadation of Insects and their embryonic 

 growth I have illustrated fully in a special paper.^^^ Similar com- 

 parisons have been made in the class of Fishes; among Reptiles, we 

 find the most striking examples of this kind among Batrachians (see 

 above, Sect, xii); among Birds^^^ the uniformly webbed foot in all 

 young exhibits another correspondence between the young of higher 

 orders and the permanent character of the lower ones. In the order 

 of Carnivora, the Seals, the Plantigrades, and the Digitigrades ex- 

 emplify the same coincidence between higher and higher representa- 

 tives of the same types, and the embryonic changes through which 

 the highest pass successively. 



No more complete evidence can be needed to show that there 

 exists throughout the animal kingdom the closest correspondence 

 between the gradation of their types and the embryonic changes 

 their respective representatives exhibit throughout. And yet what 

 genetic relation can there exist between the Pentacrinus of the 

 West Indies and the Comatulae, found in every sea; what between 

 the embryos of Spatangoids and those of Echinoids, and between the 

 former and the adult Echinus; what between the larva of a Crab and 

 our Lobsters; what between the Caterpillar of a Papilio and an adult 

 Tinea, or an adult Sphinx; what between the Tadpole of a Toad and 

 our Menobranchus; what between a young Dog and our Seals, unless 

 it be the plan designed by an intelligent Creator? 



SECTION XXVIII 



RELATIONS BETWEEN THE STRUCTURE, THE EMBRYONIC GROWTH, 



THE GEOLOGICAL SUCCESSION, AND THE GEOGRAPHICAL 



DISTRIBUTION OF ANIMALS 



It requires unusual comprehensiveness of view to perceive the 

 order prevailing in the geographical distribution of animals. We 

 should therefore not wonder that this branch of Zoology is so far 



^" The Classification of Insects from Embryological Data (Smithsonian Contributions 

 to Knowledge, II, Washington, 1850). 

 1*^ Agassiz, Lake Superior . . . (Boston, 1850), p. 194. 



