164 LECTURES. 



them, connecting types with embryonic characters. This is not an 

 isolated fact, hut one which meets us at every step in the course of our 

 study of the geologic history of the earth. It is hut one illustration 

 of a general latv, a law of the deepest philosophic import, and yet one 

 which is still very imperfectly recognized among geologists. The law 

 may he thus stated : The first introduced animals or plants of any 

 class have heen combining types, i. e., have united within themselves 

 the characters of several families, now distinct and even widely sepa- 

 rated. Thus the first vertebrates introduced were fishes, but not 

 typical fishes, as we might be led a priori to expect, but Placoids and 

 Ganoids, families which, particularly in their earlier lepresentatives, 

 united with ordinary fish characters others which connected them with 

 the class of reptiles, and even of mammals; and still others which 

 connect them with the embryonic condition of the typical fishes. It is 

 this combination of embryonic characters with others which connect 

 them with the higher classes, this union of high and low characters, 

 which has given rise to all the disj)ute concerning the position of these 

 families in the scale of Fishes as well as to much of the difi'erence of 

 opinion concerning the law of succession of animals in Greology. 

 Again, the first introduced reptiles, viz: the reptiles found in the old 

 red sandstone and coal, are the most remarkable instances of con- 

 necting types of which we have any knowledge. In the first place 

 they seem to have been amphibious, (in the proper sense of the word,) 

 and thus to have connected land animals and water animals, air 

 breathing with water breathing, and all of them united characters, 

 which are now represented by widely separated families. To give a 

 single instance : the carboniferous reptile, recently described by Pro- 

 fessor Wyman and exhibited at the last meeting of the Scientific As- 

 sociation at Albany, so remarkably combined characters which are now 

 parcelled out between the three families of Batrachians, Saurians, and 

 Ophidians, that this distinguished comparative anatomist seemed 

 almost at a loss as to which of these iamilies to assign it. He decided, 

 however, that it most nearly resembled a Salamandroid Batrachian 

 with characters closely connecting it with the other families already 

 mentioned. 



The LahyrintJiodon of the new red sandstone has been classed by 

 some anatomists with Boiracliians, and by others with crocodiles. 

 There seems yet a doubt whether it should be called a tailless croco- 

 dile or a crawling frog with crocodilian teeth. The huge Saurians of 

 the secondary period combined reptilian with fish, and even some 

 mammalian characters. Even in the tertiary period and in the intro- 

 duction of the highest animals this law is not forgotten. The recent 

 investigations of Professor Owen have shown that the first introduced 

 Pachyderms were not typical Pachyderms, but that they combined the 

 characters of Pachyderms and Ruminants to such a degree that it is 

 almost impossible to assign them with certainty to one or the other 

 order. In fact, the study of these extinct forms has led this great 

 anatomist to class the Pachyderms and Ruminants together as sub- 

 divisions of one and the same order. 



Thus in every case in the earliest faunas and florae one class stood 

 for many. The earliest families combined the characters of several 



