1902,] NATURAL SCIENCES OF PHILADELPHIA. 217 



To commence with Ihe smallest perceptible parts of the organiza- 

 tion, the components of the cell. A classifi cation limited to these 

 would represent the facts of cellular structure, and might l)e 

 based upon the finer cytoplasmic structure, upon the number and 

 nature of centrosomes or chromosomes, etc. But it is clear that 

 such a classification, even if it could be consequently perfected, 

 would be no classification of the organization as a whole, for it 

 would neglect the structure and grouping of the more complex 

 jDarts of the body. In thus affording no representation of the 

 whole organization, it would be contrary to the conclusion that the 

 organization (organism) as a whole miLst be considered, and hence 

 would not be allowable.'" The same argument holds also for a 

 classification based upon kinds of tissues. These two possible 

 modes of classification need not confuse the phylogenist, for they 

 are logically incorrect. 



There now arises the more difiicult question. What particular 

 category of the more complex parts of the organization should be 

 considered ? Under these are the organs (as this term is generally 

 used), the organ systems and the larger divisions of the body, such 

 as antimeres, metameres, right and left side, etc. These being the 

 larger structural complexes, their facts of structure show the organi- 

 zation as a whole, and hence on them the classification must be 

 made. But should the facts of body plan, such as radiality or 

 metamerism, be ascribed greater value than the facts of the organs 

 which compose them ? Or otherwise expressed, is structure or 

 arrangement of the parts to be first considered ? The answer to 

 this must be empirically determined, and by determining which of 

 the two is the more conservative, the structure of the organ or its 

 spatial relations in the whole organization. 



A little reflection upon the facts of comparative anatomy shows 

 that " body plan " is generally very far from conservative. For, 

 in the first place, different body plans or modes of arrangement of 

 the parts are frequently found in different parts of the same organ- 

 ism. Thus in some Cestoda the scolex is more or less radial with 

 regard to the arrangement of its parts, while each proglottid of the 

 trunk may be bilaterally symmetrical (^Dlpylidium). In the 



"^ Necessarily the Metazoa only are meant, for with the Protozoa there 

 can be no other than a cellular classification : yet. even in these, the 

 organization as a whole must be considered. 



