14 Mr. R C. Punnett. On the Composition and Variations 



This table shows that on the average the male possesses 0'3 of a 

 whole vertebrae less than the female. It has already been shown that 

 the position of the pelvic girdle in the male is on the average 0'82 

 metamere more rostral than in the female. The interesting question 

 of the correlation between the number of whole vertebrae and the 

 position of the pelvic girdle, will be examined in more detail later on 

 in this paper. 



In bringing these statistics to a close, the question suggests itself 

 which of the two sexes is the more variable 1 To attempt to answer 

 this, I have calculated the standard deviation (o-) and also the prob- 

 ability error (E) for the two sexes on the following points : 



Table VII. 



From this table it will be seen that the variability of the female is 

 greater on three of the above points, viz., with regard to (1) the serial 

 number of the first girdle-piercing nerve, (2) the number of post-girdle 

 nerves, and (3) the number of the whole vertebrae ; whilst on the 

 remaining point the number of the collector nerves, the male shows 

 a slightly greater variability, though here the two sexes are almost on 

 an equality. Of course it must be borne in mind that the numbers 

 dealt with are small for applying this method. Still the differences in 

 the two sexes are fairly well marked, particularly in the case of the 

 whole vertebras, where the standard deviation in the female pre- 

 ponderates even when the maximum allowance is made in each sex for 

 the probable error. 



Having now concluded these statements on the amount of variation 

 involved on the various points enumerated, we shall next enquire into 

 the possibility of establishing any correlations between the position 

 of the girdle and other points of variation. 



A. Between the First Girdle-piercing Nerve and the Number of Collector 



Nerves. 



As the nerves which take part in the formation of the collector are 

 only concerned in the innervation of muscles connected with the most 



