BOTANY. [chap. 



backwards from the most highly developed forms of each, 

 we come in the end to a series of living organisms in 

 which those peculiarities that give individuality to plants 

 and animals respectively are absent; such organisms 

 are included in a group known as the Protozoa, the 

 simplest representatives of which are amongst the most 

 primitive of living bodieSj and at the point where the 

 plant and animal kingdoms appear to converge, consist- 

 ing of exceedingly minute portions of protoplasm without 

 any external protecting cell-wall^ and furnished with one 

 or more exceedingly slender prolongations or cilia for 

 purposes of locomotion ; such infinitesimal organisms are 

 spoken of as the Flagellate Protozoa, from the presence 

 of the cilia or flagellse alluded to above. 



The Protozoa, in common with all primitive types, are 

 aquatic in habitat, feed on organic food, and are generally 

 considered by zoologists as representing the starting 

 point of the Animal Kingdom, and certainly as one of 

 the radiating branches from this primordial group be- 

 comes more and more differentiated, we observe the 

 characteristics that become slowly evolved in each suc- 

 ceeding group to constitute collectively those structures 

 and functions which give individuality to the Animal 

 Kingdom, and may be briefly enumerated as follows. 



From a comparatively neutral starting point in the 

 sense of presenting the minimum known amount of dif- 

 ferentiation and division of labour, the most important 

 feature evolved by the members of the Animal Kingdom 

 is the specialization of structures that enables them to feed 

 on organic matter taken into the body in the solid form. A 

 second feature is the gradual evolution of the nervous 

 system, which culminates in the higher groups in the 



