352 ESSAY ON CLASSIFICATION, 



curacy and clearness, to present a condensed account of 

 those opinions with which he disagreed, in these words: 



"Few views of the relations existing in the organic 

 world have received so much approbation as this: that 

 the higher animal forms, in the several stages of the deve- 

 lopment of the individual, from the beginning of its exist- 

 ence to its complete formation, correspond to the perma- 

 nent forms in the animal series, and that the development 

 of the several animals follows the same laws as those of 

 the entire animal series; that consequently the more 

 highly organized animal, in its individual development, 

 passes, in all that is essential, through the stages that are 

 permanent below it, so that the periodical differences of 

 the individual may be reduced to the differences of the 

 permanent animal forms." 



Next, in order to have some standard of comparison 

 with his embryological results, he discusses the relative 

 position of the different permanent types of animals as 

 follows : 



" It is especially important that we should distinguish 

 between the degree of perfection in the animal structure 

 and the type of organization. The degree of perfection 

 of the animal structure consists in the greater or less 

 heterogeneousness of the elementary parts, and the sepa- 

 rate divisions of a complicated apparatus, in one word, 

 in the greater histological and morphological differentia- 

 tion. The more uniform the whole mass of the body is, 

 the lower the degree of perfection: it is a stage higher 

 when nerve and muscle, blood and cellular tissue, are 

 sharply distinguished. In proportion to the difference 

 between these parts is the development of the animal life 

 in its different tendencies; or, to express it more accu- 

 rately, the more the animal life is developed in its several 



