III. 



CLASSIFICATION OF ANIMALS FROM EMBRYONIC 

 AND PALEOZOIC DATA. 



For several years I have been in the habit of illustrating, in my 

 public lectures and elsewhere, principles which have not yet been 

 introduced in our science, and to which I feel it my duty to call 

 attention in a more formal manner on this occasion, as during our 

 excursion we had several opportunities to discuss them at length. 

 These remarks will form an appropriate introduction to the lists of 

 the animals found about Lake Superior, which are given below. 



The principle which has regulated our classifications for the last 

 half century, is that which Cuvier worked out by his anatomical 

 investigations ; I mean the arrangement of the whole animal kingdom 

 according to the natural affinities of animals as ascertained by the 

 investigation of their internal structure. This fruitful principle, 

 applied in various ways, has produced a series of classifications, 

 agreeing or differing more or less in their outlines, but all resting 

 upon the idea, that a certain amount of anatomical characters may 

 be easily ascertained, expressing the main relations which exist natu- 

 rally among animals, and affording a natural basis for classification. 

 Structure, therefore, internal as well as external, is, according to the 

 principles of Cuvier, the foundation of all natural classifications ; and 

 undoubtedly his researches and those of his followers have done more, 

 in the way of improving our natural methods, than all the efforts of 

 former naturalists put together ; and this principle will doubtless 

 regulate, in the main, our farther efforts. 



Nevertheless, so much is left in this method to the arbitrary deci- 

 sion of the observer, that it would be in the highest degree desirable 



