however, he suggested distinguishing the degree of develop- 

 ment of the animal body and the type of organization^ 

 (Sch. V 3 a,b, 207, 208). 



By degree of differentiation Baer meant the degree of 

 heterogenity of its component parts or the degree of 

 histological and morphological differentiation. Baer con- 

 siders a higher organization where "the different divisions 

 of systems of organs are not similar to each other, and 

 each part has a more remarkable individuality," in contrast 

 to forms in which "all the organization as a whole is more 

 homogeneous." Comparing the lower vertebrates (fish) with 

 the higher arthropods (insects) reveals a greater hetero- 

 geneity of structure in the latter, although fish are a 

 higher type in organization. 



By type, Baer meant the character of distribution of 

 organic elements and organs, which represent an expression 

 of "the main relations between individual features of life 

 of the organisms." The possibility of distinguishing "type" 

 from "degree of differentiation" leads to the conclusion 

 that one type can cover different degrees of development, 

 and, on the contrary, one stage of development can be reached 

 by different types. The combination of the type with a 

 particular degree of differentiation or degree of development 

 produces the major groups of the animal kingdom, the classes. 



The confusion of the type and degree of development 

 represented, in Baer's opinion, the source of incorrect 

 classification. Clear demarcation leads to the conclusion 

 that the different forms of animals could not be put in one 

 line of development "from the monad to the human." 



Between the irain types, in Baer's words, there are 

 "intermediate forms, in which the characteristic features of 



11. On the necessity of differentiating these two under- 

 standings , Baer remarked in a more easily understood 

 report — "Beitrage zur Kenntniss der niedern Thiere . " 

 (NOVA ACTA PHYSICO-MEDICA ACADEMIAE CAESAREAE 

 LEOPOLDINA CAROL INAE NATURAE CURIOSORUM, 13 

 (1827) , pp. 525-762) , especially in the article "liber 

 die Verwandschaftsverhaltnisse der niedern Thierformen" 

 (pp. 731-762). 



352 



