2 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



The present work is concerned only with Animals ; 

 but, as there is a fundamental resemblance between 

 Plants and Animals, it is in the first place necessary 

 to enquire into the characters and modes of activity 

 of living matter, pure and simple, without any ques- 

 tion as to whether it be animal or vegetable. 



LIVING MATTER. 



Animals and plants have at least this in common, 

 that they are both fashioned out of a material which, 

 in all its essential characters, is common to them 

 both ; and, whether one would be a zoologist, or student 

 of animals, or a botanist, or student of plants, it is, 

 in the very tirst place, necessary that he should have 

 some clear and exact comprehension of what are the 

 characters and what are the modes of action of that 

 primary fashioning substance which forms the material 

 basis of living creatures, and which is known as 

 protoplasm. The fact that the sciences of zoology 

 and botany have to do with this -'physical basis" of 

 living matter separates and distinguishes them at once 

 from such studies as chemistry or physics, with which 

 the phenomena of life have no necessary connection. 



Living is distinguished from, not-living matter 

 by several important and easily recognisable charac- 

 ters. It would seem to have a fundamental and 

 characteristic composition ; it has the power of con- 

 tinuing to exist by taking into (nutrition), and 

 making part of itself (assimilation) other living or 

 even not-living matter. Nutrition and assimilation 

 lead to growth, and this growth is succeeded by a 

 stage in which the additional material obtained is 

 used for the purposes of reproduction. After a 

 tinie a living organism may be seen to be unable to 

 withstand the action of the surrounding forces in the 

 midst of which it has lived, grown, and reproduced 

 itself; in other words, its activity diminishes and 



