GENERAL ZOOLOGICAL FACTS AND THEORIES 281 



viduals of the same species, if examined closely, will also be found 

 to vary in certain respects; and even the offspring of the same 

 parents differ from one another to a greater or less degree. 

 The difference between child and parent and between children is 

 called variation. Variations are important in any discussion of 

 evolution and heredity, since their origin and influence upon the 

 transmutation of species constitute the fundamental problems 

 that are occupying the attention of philosophical zoologists at 

 the present time. 



CONTINUOUS OR FLUCTUATING VARIATIONS. If a hundred men 

 are gathered at random, and arranged in a row according to their 

 heights, it will be found that they decrease gradually from the 

 tallest at one end to the shortest at the other. This is an illus- 

 tration of continuous variation. If now we examine this line 

 more closely, we will find that the greatest number measure about 

 sixty-five inches in height, and that the number of any height 

 decreases as the ends of the line are approached. The measure- 

 ments decrease or increase gradually from the central mean to 

 one end or the other, and as many variations will be found above 

 the mean as below. The offspring of any of the individuals 

 selected will show a variability that is similarly fluctuating, and 

 follows the law of probabilities. This law holds that slight 

 modifications from the mean are most abundant, and that the 

 greater the variation, and the nearer the extremes are approached, 

 the less numerous the modifications become. 



DISCONTINUOUS VARIATIONS. Animals known as " sports," 

 " saltations," or " mutations " are examples of discontinuous 

 variability. These differ from continuous variations in that they 

 are able to transmit their differences from the mean to their de- 

 scendants. Some of the most noted sudden variations are the 

 hornless cattle of Paraguay, the niata breed of oxen of South 

 America, and the mauchamp and ancon sheep. The last-named 

 originated from a ram with crooked legs and a long back, that was 

 born in Massachusetts in 1791. When crossed with common 

 sheep, his peculiar characteristics reappeared in the offspring, 



