VI. Biology. VII, Geographical Distribution of Animals. 73 



which, live in earth or on plants (moss). Most animals^ however^ 

 die when water is withdrawn to any considerable extent, whilst many 

 [e.g., Gastropods) sustain no injury from a slight deprivation. 



Whilst some animals can scarcely live a day without food, others 

 can endure hunger for a considerable time without injury: 

 ProgSj snakes, and many others can live several months without 

 food. Sometimes animals can hold out for a very long time if they 

 are supplied Tvith water alone, although they soon die if this can- 

 not be obtained. Many fast periodically ; the periods of rest in 

 particular, which so many undergo, are simultaneous with periods 

 of starvation. It has been shown for some Fish (Salmon) that 

 before, or during, the breeding season they take no food for many 

 weeks, and the digestive tract becomes quite shrunken up : the same 

 thing, occurs also in certain other forms. Moreover, many Insects, 

 in the perfect state (which is here the breeding time also), can 

 take no food on account of the rudimentary condition of their 

 mouth-parts. During the period of starvation the body naturally 

 loses in weight, for oxidation of the tissues still continues. Often 

 when such a period approaches, masses of fat are stored up in the 

 body, and are consumed whilst it lasts (Bears, Insect-larvffi before 

 pupation) ; or reserves may be provided in other ways (crystalline 

 style of Lamellibranchs) . 



Whilst many animals, if deprived of oxygen, die instanta- 

 neously, or after a few minutes, there are others which can 

 dispense with it for a considerable time, even for many days. 

 Such animals as the Frog, indeed, can live in an atmosphere 

 destitute of oxygen : only after several hours does a certain dulness 

 occur, followed by an apparent death, from which the frog can 

 recover if it has not continued too long. Many Insects, Worms, etc., 

 exhibit a similar peculiarity. Since the production of carbon- 

 dioxide continues, combustion must be carried on by means of 

 the oxygen stored up in the cells. 



VII. The Geographical Distribution of 

 Animals. 



When the great divisions of the surface of the earth are compared 

 with one another, it is found that animal life is possessed of a consider- 

 able diversity of character, and this is true for different land faunas 

 (including fresh-water), as well as for marine. The animals which 

 live in South America are different from those inhabiting Europe; 

 the fauna of the Bast Indian coasts differs from that occurring round 

 Europe, and so on. 



