948 MR. H. H. BniNDLEY ON REPRODUCED [Dec. 1 3, 



application to the present case reads as follows : — For every unit 

 of absolute length that a particular tarsal joint deviates from the 

 mean length of such joints in the series examined, any other joint 

 selected will on the average deviate from the mean length of such 

 joints to the extent of .v units and in the same direction, [.c would 

 be equivalent to unity only in the hypothetical case of the two 

 joints always varying exactly together, or, in other words, exhibiting 

 an absolute correlation.] 



Table G. — Perijylancta americana. 



5-jointed tarsi. 



The deviation oij^ from its mean being 10, the mean of the corresponding 



deviations of _/., from its mean was •.52. 

 „ Ji „ „ I'O, the mean of the Corresponding 



deviations of^, from its uitan waa •72. 

 >i )2 " >' I'O, the mean of the corresponding 



deviations oiy. from its mean vcas -ol. 

 or, expressed conversely, 



The deviation o{j2 from its mean being l^O, the mean of the corresponding 



deviations oi'j\ from its mean was "52. 

 „ j\ „ „ ro, the mean of the corresponding 



deviations of jj from its mean was '72. 

 „ 75 „ ,, I'O, the mean of the corresponding 



deviations of J., from its mean was "31. 

 4-jointed tarsi. 

 The deviation of J, from its mean being 1-0, the moan of the corresponding 



deviations of J„ from its mean was •70. 

 „ J I „ ,, IV, the mean of the corresponding 



deviations of J^ from its mean was '60. 

 ,, Jj „ ,, ] 0, the mean of the coiTesponding 



deviations ot J^ from its mean was '49. 

 or, expressed conversely, 



The deviation of J, from its mean being 1-0, the mean of tlie corresponding 



deviations of J, from its mean was '70. 



„ J, „ ,, I'O, the mean of the corresponding 



deviations of J, from its mean was "61). 



,, J4 .. „ ro, the mean of the corresponding 



deviations of J, from its mean (vas "49. 



The number of cases on which the above results are based is of 

 course much smaller than is usually adopted for the consideration 

 of normal correlated structures on such lines, but it serves to show 

 the similarity of behaviour of the two kinds of tarsi. The specially 

 rapid growth of regenerated appendages has been referred to 

 already, and the following observation on Periplaneta emphasizes 

 the specialized nature of the regenerated limb by indicating that 

 the rate of growth is controlled according to the age of the animal 

 at the time of injury. 



20 adults of F. americana were found with the third pair of legs 

 bearing on one side a normal and on tlie other a 4-jointed tarsus. 

 The percentage difference in total length of the tarsi of the two 

 kinds averaged only 3"5, an amount not appreciable to the naked 

 eye. Now it is not at all likely that in all these cases the repro- 



