CHAPTER IV. 

 THE MORPHOLOGICAL COMPOSITION OF ANIMALS. 



199. WHAT was said in 180, respecting the ultimate 

 structure of organisms, holds more manifestly of animals 

 than of plants. That throughout the vegetal kingdom the 

 cell is the morphological unit, is a proposition admitting of a 

 better defence, than the proposition that the cell is the mor 

 phological unit throughout the animal kingdom. The qualifi 

 cations with which, as we saw, the cell-doctrine must be 

 taken, are qualifications thrust upon us more especially by 

 the facts which zoologists have brought to light. It is 

 among the Protozoa that there occur numerous cases of vital 

 activity displayed by specks of protoplasm ; and from the 

 minute anatomy of all creatures above these, up to the Tvleozoa, 

 are drawn the numerous proofs that non-cellular tissues may 

 arise by direct metamorphosis of structureless colloidal sub 

 stance. 



Our survey of morphological composition throughout the 

 animal kingdom, must therefore begin with those undiffer- 

 entiated aggregates of physiological units, out of which are 

 formed what we call, with considerable license, morphological 

 units. 



200. In that division of the Protozoa distinguished as 

 Rhizopoda, are presented, under various modifications, these 

 minute portions of living organic matter, so little different!- 



