Page:Proceedings of the Royal Society of London Vol 69.djvu/22

14 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.

No. of cases in each sex.

ff.

c?. E.

cr.

?. E.

100

0-99

0-066

0-96

0-064

100

0-8(5

0-058

0-96

-064

50

0'98

0-093

1-29

0-122

Serial number of 1st girdle- piercitig nerve

100

0-99

0-066

1-09

0-073

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