278 M. straus-durckheim's 



to the organization of the invertebrated, all those organs and 

 functions which are, more or less, invariably sustained in the 

 first division, have been regarded as fundamental ; and for this 

 sole reason, the same importance in classification has been 

 attributed to them throughout the whole animal kingdom. 

 From this course of proceeding there naturally has resulted 

 approximations, more or less systematic, which break the 

 natural relationship of many divisions. For example, — in the 

 first great division of animals, respiration and circulation being 

 in fact two functions, to which all the rest are, more or less, 

 subordinate, it has been imagined that we ought to regard 

 them as essential in the whole series of animals, and employ 

 them as the sole basis of classification. Amongst most other 

 animals, on the contrary, these functions being only secondary, 

 this principle has led to fresh errors and contradictions ; for it 

 often happens that some one family of Invertebrata, which 

 respires hy branchiae, cannot be separated from another family 

 in which the respiration is pulmonary or trachean, without 

 violating relationships depending on most of the other organs. 

 If this truth had been recognized, the Mollusca would not 

 have been placed before the articulated animals, which are, in 

 fact, the most perfect of the Invertebrata. On the other 

 hand, whatever system we might wish to establish, we could 

 never separate the Pulmonary from the Trachean Arachnida, or 

 the Branchiferous from the Pulmonary Gasteropod Mollusca. 



It has, moreover, been admitted that animals form a decreas- 

 ing series from man to the lowest zoophytes ; and, as in the 

 first class of Vertebrata, which was the best known, the most 

 perfect species is found placed precisely at the head of the 

 scale, the other divisions have also been made to commence 

 with the most perfectly organized species. In consequence of 

 this the larger divisions have been made to appear isolated 

 groups, between which any regular transition seems quite im- 

 possible. But the true cause of these sudden transitions is 

 only the too regular degradation which it has been wished to 

 introduce into each division separately, as well as to the prin- 

 ciple of the pre-eminence of organs, which has been too much 

 generalized. 



Moreover, animals have been mostly classed in a simple 

 series, although a rigorous observation proves that the natural 

 method is ramose, as was first pointed out by Lamarck. 



