LEADING GROUPS OF EXISTING SYSTEMS 141 



ence, in the former, of those masses forming mainly the bulk of the 

 body, which consist of flesh and bones as well as blood and nerves 

 and constitute another of the leading features distinguishing Verte- 

 brata and Invertebrata. Ehrenberg presents the same relations be- 

 tween the same beings as expressed by their nervous system. If we 

 now take the expressions of Aristotle, Lamarck, Oken, and Ehren- 

 berg together, have we not, as characteristic of their systems, the very 

 words by which every one distinguishes the most prominent features 

 of the body of the higher animals, when speaking of blood relations, 

 of blood and bones, or of having flesh and nerve? 



Neither of these observers has probably been conscious of the iden- 

 tity of his classification with that of his predecessors; nor indeed 

 should we consider either of them as superfluous, inasmuch as it 

 makes prominent, features more or less different from those insisted 

 upon by the others; nor ought any one to suppose that with all of 

 them the field is exhausted and that there is no more room for new 

 systems upon that very first distinction among animals.^ As long as 

 men inquire, they will have opportunities to know more upon these 

 topics than those who have gone before them, so inexhaustibly rich 

 is nature in the innermost diversity of her treasures of beauty, order, 

 and intelligence. 



So, instead of discarding all the systems which have thus far had 

 little or no influence upon the progress of science, either because 

 they are based upon principles not generally acknowledged or con- 

 sidered worthy of confidence, I have carefully studied them with the 

 view of ascertaining whatever there may be true in them, from the 

 stand-point from which their authors have considered the animal 

 kingdom; and I own that I have often derived more information 

 from such a careful consideration than I had at first expected. 



It was not indeed by a lucky hit, nor by one of those unexpected 

 apparitions which, like a revelation, suddenly break upon us and 

 render at once clear and comprehensible what had been dark and 



^ By way of an example I would mention the mode of reproduction. The formation 

 of the egg in Vertebrata; its origin in all of them in a more or less complicated Graafian 

 vesicle, in which it is nursed; the formation and development of the embryo up to a 

 certain period, etc., etc., are so completely different from what is observed in any of 

 the Invertebrata, that the animal kingdom, classified according to these facts, would 

 again be divided into two great groups corresponding to the Vertebrata and Inverte- 

 brata of Lamarck, or the Flesh- and Gut-Animals of Oken, or the Enaima and Anaiina 

 of Aristotle, etc. 



