THE MODERN ZOOLOGICAL SYSTEM 301 



the French, English, Russian and American governments to different 

 parts of the world, especially to the tropical oceans. Of these voyages 

 perhaps the most interesting were that of the Eussian ship Rurik from 

 1818 to 1820, in which Chamisso and Eschscholtz went as naturalists 

 and discovered the alternation of generation of Salpa, that of the Eng- 

 lish ship Beagle between 1831 and 1835 with Darwin as naturalist, and 

 the American expedition under Captain Wilkes between 1838 and 1842 

 with James Dwight Dana as the principal naturalist. 



The influence of all these investigations, and also of the newly es- 

 tablished cellular theory of the structure of plants and animals, on the 

 development of the zoological system led to the third great reform of 

 the latter. In 1845 von Siebold subdivided Cuvier's fourth type, the 

 Zoophyta or Eadiata, into three types or phyla, the Protozoa, Zoo- 

 phyta and Vermes, confining thus the term Zoophyta to the truly 

 radiate animals. He also broke up Cuvier's second type Articulata, re- 

 moving the Annelida to the new phylum Vermes and creating another 

 new phylum for the Crustacea, Arachnida, Myriapoda and Insecta 

 which he called the Arthropoda. Two years later E. Leuckart broke 

 up the Zoophyta, subdividing it into the phyla Echinodermata and 

 Coelenterata, and emphasized the isolated position of the Protozoa, and 

 a little later Milne-Edwards added still another new type or phylum, 

 the Molluscoidea, in which he included the Bryozoa, Brachiopoda and 

 Tunicata. The animal kingdom was thus in 1850 subdivided into 

 eight phyla, the Protozoa, Echinodermata, Vermes, Arthropoda, Mol- 

 luscoidea, Mollusca and Vertebrata, an arrangement which is still 

 found in many text books. 



Darwin's " Origin of Species " was published in 1859 and the 

 fourth and last important reform of the zoological system of classifica- 

 tion was the direct consequence of the doctrines therein promulgated. 

 The theory of the common descent and blood relationship of all animals 

 which Darwin taught was at variance with Cuvier's theory of fixed 

 types and in harmony with Lamarck's theory of the essential unity of 

 the animal kingdom, and was first employed by Haeckel as the basis of 

 a system of classification. In 1877 he called attention to the need of 

 placing the entire system on an evolutionary basis and at the same time 

 subdivided the animal kingdom into the two great groups of the Pro- 

 tozoa and the Metazoa, and the latter into the two great groups of the 

 Coelenterata and the Coelomata. In still more recent times other au- 

 thors, notably Hatschek, following Haeckel's lead, have carried the sub- 

 division still further on the same basis. The old idea of types, however, 

 has a very tenacious life and is still the basis of the classification of 

 animals in most text-books — and probably rightly so. For most ani- 

 mals, notwithstanding their ultimate relationships with one another, 

 can as a matter of fact be grouped in a number of distinct types or 



