A FEW FACTS ABOUT ZOOLOGY. 13 



Recapitulation. 



The radiates, mollusks, articulates, vertebrates. There are 

 tiny animals whose existence is only made known by the 

 microscope ; the term infusoria is applied to many of these 

 because they abound in any infusion of matter which is al- 

 lowed to putrefy. Misguided by their seeming simplicity of 

 structure, Cuvier placed all these in the lowest division, the 

 radiata. 



These animalcules are like transparent little globules, and 

 seemed to have no special organization. Further study and 

 improvements in the microscope have proved that they in- 

 cluded a great variety of beings, some of them belonging to 

 the mollusks, others to the articulate type; being, in fact, 

 microscopic shrimps, and so far from being a class by them- 

 selves, they seem to comprise representatives of every class 

 except the vertebrates. In these investigations many of 

 these infusoria have been found to be vegetable in their 

 nature. 



Still many naturalists have insisted upon a fifth division, 

 lower than the radiata, called the protozoa. "This division 

 has been proposed to contain that vast cloud of miscroscopic 

 beings on the verge of the animal kingdom which could not 

 be received into either of the subkingdoms." Protozoans, 

 we are told, have no 

 organs ; they could 

 not be more simple. 

 They are devoid of 

 muscle, nerves, 01 

 stomach ; they are 

 as structureless as a 

 drop of jelly ; they 

 feel without nerves, 

 move without mus- fig, 9. 



cles, and digest without a stomach. In Fig. 9 we have a 

 picture of an animal of this kind; it is so constantly altering 



