MORPHOLOGY AND PHYSIOLOGY. II 



Finally, it is worthy of notice that it is in their lower and 

 not in their higher developments that the two kingdoms of 

 organic nature approach one another. No difficulty is ex- 

 perienced in separating the higher animals from the higher 

 plants, and for these universal laws can be laid down to which 

 there is no exception. It might, not unnaturally, have been 

 thought that the lowest classes of animals would exhibit most 

 affinity to the highest plants, and that thus a gradual passage 

 between the two kingdoms would be established. This is not 

 the case, however. The lower animals are not allied to the 

 higher plants, but to the lower ; and it is in the very lowest mem- 

 bers of the vegetable kingdom, or in the embryonic and imma- 

 ture forms of plants little higher in jthe scale, that we find such 

 a decided animal gift as the power of independent locomotion. 

 It is also in the less highly organised and less specialised forms 

 of plants that we find the only departures from the great laws 

 of vegetable life, the deviation being in the direction of the 

 laws of animal life. 



5. MORPHOLOGY AND PHYSIOLOGY. 



The next point which demands notice relates to the nature 

 of the differences between one animal and another, and the 

 question is one of the highest importance. Every animal 

 as every plant may be regarded from two totally distinct, 

 and, indeed, often apparently opposite, points of view. From 

 the first point of view we have to look simply to the laws, 

 form, and arrangement of the structures of the organism ; in 

 short, to its external shape and internal structure. This con- 

 stitutes the science of morphology ({tootp^form, and Xo'yoj, dis- 

 course}. From the second, we have to study the vital actions 

 performed by living beings and \hz functions discharged by the 

 different parts of the organism. This constitutes the science 

 of physiology. 



A third department of zoology is concerned with the relations 

 of the organism to the external conditions under which it is 

 placed, constituting a division of the science to which the term 

 " distribution " is applied. 



Morphology, again, not only treats of the structure of living 

 beings in their fully developed condition (anatomy), but is 

 also concerned with the changes through which every living 

 being has to pass before it assumes its mature or adult charac- 

 ters (embryology or development). The term " histology " is 

 further employed to designate that branch of morphology which 

 is specially occupied with the investigation of minute or micro- 

 scopical tissues. 



