124 HYPOTHESIS OF THE DEVELOPMENT OF 



at any period solely by negative evidence, all other students of 

 this science seeing very well that, though in the geological 

 record there must be many blanks, there can be none extend- 

 ing to whole sub-kingdoms and classes. 



It is equally clear, and can now be asserted on the autho- 

 rity of the first naturalists of the age, that, in all the con- 

 spicuous orders of animals, there have been, in the progress of 

 time, strong appearances of a progress of forms, from the more 

 simple to the more complex, from the more general to the 

 more special, the highest and most typical forms being always 

 attained last. It cannot be pretended, in all cases, that we 

 have an unbroken and perfect series, exhibiting these grada- 

 tions, for the Stone Book is one wanting many leaves ; but in 

 the orders that have been best preserved, there is such a 

 well-marked succession leading on from one degree of organi- 

 zation to another, that the general fact of a progress in all the 

 orders is not to be doubted. Thus the examples of the 

 cephalopodous, gasteropodous, and bivalve orders of mollusca 

 found in the Silurian formation, are all of them of humble 

 character, standing low, as it were, in their respective lines of 

 development. These were succeeded in the higher formations 

 by superior genera. It is the same with the well-marked line 

 of the echinodermata, the crinoid of the Silurians leading 

 gradually on, through a fine series of intermediate forms, to 

 the echinus of the Oolite. The cartilaginous are succeeded by 

 the osseous fishes, and in the cartilaginous order itself there 

 is a progress in the series of genera. The characters of the 

 saurian reptile first make a sort of dawn in a family of fishes j 

 then there are species half fish, half reptile ; after which comes 

 a succession of forms ending in true crocodiles. In the plants 

 of the early world, as far as they are known to us, the same 

 progress may be traced in the broad features of the succession. 



In this revelation of organic history there are some things 

 much requiring to be kept in mind. One is, that the initial 

 genera of the various orders, though always of humble organi- 

 zation comparatively, are not always liable to be described as 

 positively so. They are always perfect animals ; in many in- 

 stances they are of large bulk as compared with other genera 

 of their own orders, and are sometimes not without traits of 

 organization calculated to excite our admiration. It is per- 

 fectly evident, in all of them, that they have been well fitted 

 by creative wisdom for the part they had to play in the field 

 of life. There is need for these remarks, to prevent the reader 



