42 MANUAL OF ZOOLOGY. 



INVERTEBRATE ANIMALS, 



PROTOZOA. 



CHAPTER I. 



i. GENERAL CHARACTERS OF THE PROTOZOA. 

 2. CLASSIFICATION. 3. GREGARINID.E. 



i. General Characters. The sub-kingdom Protozoa, as the 

 name implies, includes the most lowly organised members of 

 the animal kingdom. From this circumstance it is difficult, if 

 not impossible, to give an exhaustive definition, and the fol- 

 lowing is, perhaps, as exact as the present state of our know- 

 ledge will allow : 



The Protozoa may be defined as animals, generally of minute 

 size, composed of a nearly structureless jelly-like substance (termed 

 11 sarcode"), showing no composition out of definite parts or seg- 

 ments, having no definite body-cavity, presenting no traces of a 

 nervous system, and having either no differentiated alimentary 

 apparatus, or but a very rudimentary one. 



The Protozoa are almost exclusively aquatic in their habits, 

 and are mostly very minute, though they sometimes form 

 colonies of considerable size. They are composed of a more 

 or less contractile, jelly-like substance, called " sarcode" or 

 " animal protoplasm," which is semi-fluid in consistence, and 

 is composed of an albuminous base with oil-globules scattered 

 through it. Granules are generally developed in the sarcode, 

 and in many cases there is a definite internal solid particle, 

 termed the " nucleus." 



In no Protozoan are any traces known of anything like the 

 nervous and vascular arrangements which are found in animals 



