The Simplest Animals 79 



comparison with the brains of other animals, although he 

 did not carry his studies beyond what is visible to the un- 

 aided eye. 



During the Reign of Terror in Paris, Georges Cuvier had 

 the opportunity, as tutor to the son of a count, to spend 

 half a dozen years at the seashore with plenty of time for 

 study and reflection, and with no books to tell him what to 

 think. Here he accumulated a remarkable amount of first- 

 hand knowledge of many animals lower in the scale of life 

 than fishes. Later he undertook to learn at first hand the 

 structure of representatives of " all the groups of animals." 

 He began with the lower forms, and his thoroughgoing study 

 gave him a more comprehensive view of the different orders 

 than anybody before him had attained. As an outcome of 

 many years of such study he concluded that animal life had 

 been created according to four distinct plans or types. These 

 were (i) the vertebrates; (2) the molluscs, or soft-bodied 

 animals; (3) the articulates or animals with jointed bodies; 

 and (4) the radiates, animals with parts arranged around a 

 center, like the sea-stars and jellyfish. 



Cuvier, who opposed to the end of his days the idea 

 of change in species, established the science of comparative 

 anatomy, and thus helped his successors to see more clearly 

 that evolution had in fact taken place. His was a great im- 

 provement upon earlier schemes of classification, although 

 it still left a great deal for later students to supply. His view 

 of types, with subsequent expansions, enables us to take a 

 survey of the animal world without becoming hopelessly 

 lost in the maze. 



The Simplest Animals 



We have seen (page 55) that our common notion of 

 being " alive " includes certain activities and characteristics. 

 Living things grow by assimilation, they are sensitive to ex- 

 ternal changes, they move, they throw off refuse, they breathe, 

 they reproduce, and so on. It is not necessary, however, in 



