Page:Proceedings of the Royal Society of London Vol 69.djvu/17

Rh

A considerable amount of variation occurred under this head, and the amount shown by the two sexes differs the number in the male being greater than in the female. The results may be tabulated as follows :

Tabl III.

Number of

post-girdle nerves.

<?-

Average in $ 9 '45

6

3

? 8-06

7

4

28

8

6

38

Diff 1-39

9

38

24

10

45

7

11

7

From this table it appears that there is a greater caudal extension of the fin innervation area in the male, which amounts to 1 39 meta- mere. It has, however, already been seen that in the male the pelvic girdle is on the average 82 metamere, more rostrally situated than in the female. Consequently the nett caudal preponderance of the fin innervation area in the male over that in female amounts to 1 39 - 0'82 = 0'57 metamere.

III. Variations in the number of Nerves forming the Collector. Table IV.

Number

of nerves forming collector.

<?.

Average for $ 10 '70 ? 10-69

9

12

14

10

30

24

Diff 0-01

11

36

42

12

20

19

This table shows that, whilst the number of the nerves forming th collector is subject to a considerable amount of variation, there is a striking agreement in the average number of collector nerves in the two sexes.