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SCIENCE. 



[N. S. Vol. III. No. 60. 



that extent may have led to the wider gen- 

 eralization that followed. Let all pos- 

 sible credit then be assigned to it. 



The classification of animals generally- 

 adopted, and in this country especially, up 

 to at least the early years of the present 

 ■ half century, was based on what was called 

 plan or type and was mainly due to Cuvier. 

 According to this school there were four 

 ' great fundamental divisions of the animal 

 kingdom,' and these were ' founded upon 

 distinct plans of structure, cast, as it were, 

 into distinct moulds or forms.' The term 

 generally used to designate this category 

 was branch or subkingdom and the sub- 

 kingdoms themselves were named Verte- 

 brates, Mollusks, Articulates and Radiates. 

 Various modifications of this system and 

 more subkingdoms were recognized by many 

 zoologists, but the one specially mentioned 

 was in very general use in the United 

 States because favored by Agassiz, who 

 then enjoyed a great reputation. Almost 

 all naturalists of other countries, and many 

 of this, recognized the distinctness, as sub- 

 kingdoms or branches, of the Protozoans 

 and Ccelenterates. But Huxley, in 1876, 

 went still further and segregated all ani- 

 mals primarily under two great divisions 

 based on their intimate structure, accepting 

 for one the old name. Protozoa, and for the 

 other Haeckel's name, Metazoa. 



" Among those animals which are lowest 

 in the scale of organization there is a large 

 assemblage, which either present no difier- 

 entiation of the protoplasm of the body 

 into structural elements; or, if they possess 

 one or more nuclei, or even exhibit distinct 

 cells, these cells do not become metamor- 

 phosed into tissues — are not histogenetic. 

 In all other animals, the first stage of de- 

 velopment is the differentiation of the vi- 

 tellus into division-masses, or blastomeres, 

 which become converted into cells, and are 

 eventually metamorphosed into the ele- 

 ments of the tissues. For the former the 



name Protozoa may be retained ; the latter 

 are coextensive with the Metazoa of 

 Haeckel." 



While not exactly original with Huxley, 

 the recognition of these two great categories 

 of the animal kingdom was hastened among 

 naturalists, and found place in most of the 

 works by men of authority that followed. 

 That such recognition greatly facilitates 

 morphological concepts is certain. Eut 

 most of the further new features of this 

 classification have not received the appro- 

 bation of naturalists generally. And here 

 it may be admitted that Huxley was rather 

 a morphologist in a narrow sense, or ana- 

 tomist rather than a systematist of greatly 

 superior excellence. Unquestionably he 

 did much excellent work in systematic zo- 

 ology, but the direct subject of investiga- 

 tion was perhaps treated from too special 

 a standpoint, and sometimes without an at- 

 tempt to coordinate it with the results in 

 other fields, or to measure by some given 

 standard. He was indeed a great artist, but 

 he used his powers chiefly to sketch the out- 

 lines of a picture of nature. This was done 

 with the bold and vigorous hand of a master, 

 but his productions were deficient in details 

 and finish and were sometimes imperfect on 

 account of inattention to perspective and 

 perhaps deliberate neglect of the niceties of 

 nomenclature. (And lest I may be misun- 

 derstood, let me here explain that by system- 

 atic zoology I mean the expression of all the 

 facts of structure in a form to best represent 

 the values of the differences as well as re- 

 semblances of all the constituents and 

 parts of the entire organization, from the 

 cells to the perfected organs and the body as 

 a whole.) For example, he separated Am- 

 phibians from Eeptiles and combined them 

 with Fishes, and yet under the last name 

 comprised the Leptocardiana and Marsipo- 

 branchs, and to his influence is doubtless due 

 to a large extent the persistence of English 

 (but not American) naturalists in a combi- 



