INTRODUCTION 3 



Vermes into the five classes of Mollusca, Insect a, Vermes, Echinodermata, 

 and Polypi. Thus a long step was taken towards modernizing the system, 

 and this early effort of Lamarck may be said to be the first modern classi- 

 fication of animals. He, in his later works, further subdivided the inver- 

 tebrate types until he had ten, the fundamental idea at the basis of his 

 classification being that the various groups of animals constitute a single 

 ascending series which begins with the lowest and ends with the highest. 

 This principle of the unity of the type found a wide acceptance among the 

 naturalists of that time and was based upon the law: Natura non facit 

 saltum. 



In 1812 Cuvier published his subdivision of the animal kingdom into 

 four branches or types and in 1817 his great work Le Eegne Animal, which 

 established the second great reform of the system, and was destined to 

 exert an influence only second to that of Linnaeus* Systema Naturae 

 upon the study of animals and the development of the system. In these 

 works Cuvier controverted the principle of the unity of type among ani- 

 mals and taught that, instead of one, four distinct and permanent types 

 prevail. It was upon these four types that he based his four fundamental 

 branches of the animal kingdom: Vertebrata, Articulata, Mollusca and 

 Zoopliyta or Eadiata. 



A comparison of this classification with that of Linnaeus will show 

 what a tremendous advance had been made in the development of the sys- 

 tem in the half-century separating them. The group of animals which 

 had benefited most in this general advance was probably the Mollusca, 

 which was Cuvier's special field of research. The lowest group in Cuvier's 

 system, as in that of Linnaaus, was the one about which the least was 

 known, the Zoophyta or Eadiata, being made up of several distinct and 

 heterogeneous groups of animals which bore no near relationships to one 

 another. 



This condition led to an active investigation during the generation 

 immediately following of all the lower animals, and a very large number 

 of works of fundamental importance appeared. Rudolphi studied the 

 parasitic worms, Tiedemann and L. Agassiz the anatomy and Johannes 

 Miiller the development of echinoderms, Ehrenberg the microscopic ani- 

 mals, Eschscholtz, Sars, and others jellyfish and polyps. The knowledge 

 of these two latter groups was also very much extended as the result of 

 various scientific expeditions which were sent out by the French, English, 

 Russian, and American governments to different parts of the world, espe- 

 cially to the tropical oceans. Of these voyages perhaps the most inter- 

 esting were that of the Russian ship Eurik from 1815 to 1818 in which 

 Chamisso and Eschscholtz went as naturalists and discovered the alterna- 

 tion of generations of Salpa, that of the English ship Beagle between 1831 



