CHAMBERS'S INFORMATION FOR THE PEOPLE. 



medium of protoplasm contained in its cells, it 

 combines into still more complex organic com- 

 pounds, which contribute to the development or 

 maintenance of the special specific form of the 

 organism of which it is a part. Plants can assimi- 

 late no elementary substance except oxygen, unless 

 it is presented to them in the nascent condition. 



An animal stands in exactly the same relation 

 to the binary compounds, carbonic acid, water, 

 and ammonia, which, along with salts, form the 

 food of plants. An animal cannot assimilate these 

 substances directly ; they must first be elaborated 

 to the condition of ternary and quaternary com- 

 pounds, which can be done only by the cells of 

 plants. This is the broad and practical distinction 

 between the vegetable and the animal kingdom. 

 Plants possess the power of absorbing, modifying, 

 and organising inorganic substances ; while animals 

 are entirely dependent for their support upon the 

 organic substances thus prepared. 



The pale growing parts of plants have precisely 

 the same vital properties and relations as animal 

 protoplasm. It is only in cells in which proto- 

 plasm elaborates and incorporates with itself 

 colouring-matter (endochrome), which seems to be 

 a more powerful catalytic agent, capable of dis- 

 engaging the component atoms of the more stable 

 binary compounds, when loosened by the vibra- 

 tions of light, that the special function of the 

 vegetable cell is manifested. Further, in the in- 

 terior of the cells of some plants, as Chara, the 

 movements of the protoplasm are so special and 

 characteristic as to prove its absolute identity with 

 the protoplasm of the Rhizopods. 



A living being is a complicated machine, which 

 does a great deal of various work. One of the 

 higher animals, to take an example, is made up of 

 a great many parts, each of which does its own 

 special part of that work thus, the stomach 

 digests, and the eye sees. These several parts are 

 called organs, and the thing which an organ does 

 is called its function. If we remove these organs, 

 performing each its function, one by one, the 

 whole animal disappears. The animal body 

 therefore consists of the sum of its organs. 



Living beings may be studied under three 

 principal aspects the Morphological (morphe, 

 form, and logos, a discourse), the Physiological, 

 and the Distributional. 



Morphology, which treats of the form and struc- 

 ture of living beings, includes anatomy, both 

 naked-eyed and microscopic ; to the latter, the 

 term Histology (kistos, a web, and logos) has been 

 applied. It also embraces Embryology, or the 

 study of the forms of living beings in all stages of 

 development, from their earliest or immature con- 

 dition, tiU they reach their mature or adult state. 



Physiology treats of the functions of the organism 

 as a whole, or of its separate component parts, 

 organs, or tissues ; of what an animal does, or of 

 what its different parts do. The functions of an 

 organism are divisible into i. Function of Nutri- 

 tion. 2. Function of Generation or Reproduction. 

 3. Function of Irritability or Correlation. 



The function of nutrition has reference to the 

 support and maintenance of the body. Matter is 

 introduced into the interior of the body ; there it 

 undergo.es certain changes, which assimilate it to, 

 and fit it to be incorporated with, the textures 

 which compose the body. The function of repro- 

 duction serves the purpose of perpetuating the 



130 



species. The function of nutrition and the function 

 of reproduction have been called the functions of 

 ' organic ' or ' vegetative ' life, because they are 

 possessed both by plants and animals. The func- 

 tions of relation including irritability, conscious- 

 ness, sensation, and volition, with all the move- 

 ments depending upon the will bring the organ- 

 ism into connection with the outer world, and the 

 outer world into connection with the organism, 

 so that thus the one reacts upon the other. This 

 group of functions is possessed by animals alone, 

 so that they have been called the 'functions of 

 animal life.' 



Distribution treats not only of the areas of the 

 globe over which organisms are distributed, and 

 the conditions under which they exist, but it also 

 relates to the history of life in bygone ages, as 

 furnished to us by the evidence of fossil remains. 

 The former is called distribution in space, or 

 geographical distribution ; the latter, distribution 

 in time. 



Classification. On looking at the multitude and 

 variety of animal forms around us such as we 

 are familiar with as inhabitants of this country, or 

 as natives of other climates collected for our obser- 

 vation the mind naturally associates together 

 those which have the greatest general resem- 

 blance, and separates these (although differing in 

 some degree amongst themselves) from those 

 with which they have greater dissimilarity. Now, 

 it is necessary that some system of arrange- 

 ment or classification should be adopted, by 

 bringing together those animals which most 

 closely resemble each other, not so much in 

 external appearance as in internal structure, in 

 order that the mind shall be the better able to 

 grasp the facts of zoological science. A classifi- 

 cation, therefore, will be correct in proportion to 

 the number of ascertained facts upon which it 

 is founded. Zoologists, in seeking to classify 

 animals, are in the habit of using several terms, 

 one of the most important being species. It is by 

 no means easy to define this term. It is generally 

 understood to mean an assemblage of animals 

 that resemble each other in all essential points of 

 structure, and which are supposed all to have 

 descended from the same parent stock. A test to 

 which much importance has been assigned, is 

 founded on the supposed fact, that when the 

 animals of different species breed together, their 

 offspring is barren. This offspring is called a 

 hybrid thus, a mule is a hybrid between a horse 

 and an ass. This, however, is not an absolutely 

 satisfactory or conclusive test of specific identity, 

 as hybrids between undoubtedly distinct species 

 have been known, though rarely, to breed and 

 produce fertile offspring. 



Until lately it has been the almost universal 

 belief among naturalists that species are perma- 

 nent within very narrow limits of variation ; that 

 is to say, that any group of animals which present 

 the same specific characters, characters which 

 lead an educated observer to set them down as 

 the same thing for example, all common 

 partridges, or, to take a variable species, all 

 domestic dogs are descended from an ancestry 

 which can by no possibility include anything 

 except partridges or dogs, and can never, under 

 any circumstances, or through the lapse of any 

 amount of time, give origin to anything except 

 dogs or partridges. This view, of course, involves 



