Succession of Organized Beings. 163 



deposits as they occur in various parts of Europe, we may fairly say 

 that the fossils form, in their succession, a series of progressive 

 types. 



Another example may perhaps illustrate the point more fully. 

 The orthocera of the oldest periods precede the curved lituites, which, 

 in their turn, are followed hy the circomvolute nautilus. Here, 

 again, we have a natural gradation of a series of progressive types. 

 Again, among crinoids, we find, in the older deposits, a variety of 

 species resting upon a stem, while free crinoids begin to appear only 

 during the secondary deposit and prevail, in the present creation, 

 over those attached to the soil. Here, again, we have a series of 

 progressive types developed successively, which are apparently inde- 

 pendent of each other and seem to bear no other relation to each 

 than that arising from the general character of the group to which 

 they belong. Such types exemplify simply in the groups to which 

 they belong, a real progress in the successive development of the 

 peculiarities which characterise them as natural divis'ons among ani- 

 mals. Such forms I shall call Progressive Types. 



The relations, however, which are exemplified in the oldest 

 fishes, in the ichthyosaurians, in the pterodactyls or in the mega- 

 losaurians, seem to me to be clearly of a different character, and to 

 differ from simple progressive types, inasmuch as those which appear 

 earlier, combine peculiarities which, at a later period, appear sepa- 

 rately in distinct forms. For instance, the reptilian characters 

 which we recognise in the sauroid fishes, are developed at a later 

 period in animals no longer belonging to the class of fishes, but con- 

 stituting by themselves new types, provided with additional peculi- 

 arities which separate them fully from the fishes in general, as well 

 as from those fishes in which we recognise some relation to reptiles 

 during a period when no reptile existed. 



Again, the ichthyosaurians, though true reptiles appearing long 

 after fishes had been called into existence, and during an early period 

 of the history of the reptiles, still shew their relation to fishes by the 

 character of their vertebral column, and foreshadow, as it were, in 

 their form, the cetacea of later ages, as well as many forms of the 

 gigantic saurians of the secondary period. The same may be said of 

 the pterodactyls, which are also true reptiles, but, in which the an- 

 terior extremity foreshadow peculiarities characteristic of birds and 

 bats. Such types I shall call Prophetic Types. 



To an analytic mind the examination of the peculiarities of such 

 animals may fortell a higher progress of development, carried out in 

 real existence, only during a later period, even if he had never seen 

 the later ones ; for in such types the germs of a future development 

 may be recognised, and upon close examination, truly referred to 

 the peculiarities of other higher groups, even if the intermediate 

 links remained unknown, which, however, as the matter now stands, 



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