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 quali- 

 fications 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, are drawn the numer- 

 ous proofs that non-cellular tissues may arise by direct meta- 

 morphosis of mixed colloidal substances.* 



* Since this paragraph was published in 1865, much has been learned con- 

 cerning cell-structure, as is shown in Chapter VI* of Part I. While some 

 assert that there exist portions of living protoplasm without nuclei, others 

 assert that a nucleus is in every case present, and that where it does not exist 

 in a definite aggregated form it exists in a dispersed form. As remarked in 

 the chapter named, " the evidence is somewhat strained to justify this dogma." 

 Words are taken in their non-natural senses, if one which connotes an indi- 

 vidualized body is applied to the widely-diffused components of such a body ; 

 and this perverting of proper meanings leads to obscuration of what may 

 perhaps be an essential truth. As argued in the chapter named ( 74c, 74/), 

 jclear matter is, as shown by its chemical character, an extremely unstable 

 substance, the molecular changes of which, perpetually going on, initiate 



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