72 Animal Life and Intelligence. 



noctule and the greater horseshoe bats the mean length of 

 this bone is 51*5 millimetres. The bones of each of the 

 other bats have been multiplied by such a number as will 

 bring them up to the level of size in these two species. 

 Mr. Galton, in his investigations on the variations of 

 human stature, had to take into consideration the fact that 

 men are normally taller than women. He found, however, 

 that the relation of man to woman, so far as height is 

 concerned, is represented by the proportion 108 to 100. By 

 multiplying female measurements by 1*08, they were brought 

 up to the male standard, and could be used for purposes of 

 comparison. In the same way, by multiplying in each case 

 by the appropriate number, I have brought all the species 

 in the table (Fig. 17) up to the standard of the noctule. 

 When so multiplied, the radius and ulna (selected as the 

 standard of comparison) has the same length in all the 

 species, and is hence represented by the horizontal line in 

 the table. 



Compared with this as a standard, the mean length of 

 the second metacarpal in the seven species is forty-three 

 millimetres ; that of the third metacarpal, forty-four milli- 

 metres ; and so on. The amount by which each species 

 exceeds or falls short of the mean is shown on the table, 

 and the points are joined up as before. Here, again, the 

 table gives the actual measurements in each case. For 

 example, if the mean length of the third metacarpal of the 

 greater horseshoe bat be required, it is seen by the table 

 to fall short of the mean by four horizontal divisions and 

 a quarter, that is to say, by eight millimetres and a half. 

 The length is therefore (44 — 8J) 35*5 millimetres. 



Now, it will be seen from the table that the variation in 

 the mean length of the bones in different species is much 

 greater than the individual variations in the members of 

 the same species. The table also brings out in an interest- 

 ing way the variation in the general character of the wing. 

 The noctule, for example, is especially strong in the de- 

 velopment of the second and third metacarpals, the 

 phalanges of the third digit being also a little above the 



