Page:Proceedings of the Royal Society of London Vol 69.djvu/28

20

Length and sex of specimen.

No. of nerves forming collector.

No. of nerves piercing girdle.

No. of post-girdle nerves.

No. of nerves forming posterior collector.

A. 31 mm. (?)

14

2

12

3

B. 32 ., (?)

13

2

11

3

0. 42 (?)

12

f 1 on left 1 [ 1 on right j

11

3

1). 50 ?

2 (1st girdle- piercing

10 (last small)

3

nerve on

left bv

groove)

E 62 $

2

11

3^1 Most

caudal

F 66, $

'>

11

2 branches

J- much

G-. 68 ? '

2

1 1 f last two

3 reduced

i. very

except

H. 72 ?

2

11 I small

3J in F.

Iii the younger stages, A 0, it is net possible to determine the sex as the mixipterygium is not yet distinguishable. The table brings out the following facts :

(1.) The number of nerves forming the nervus collector is greater than in older embryos or adults. This has also been shown by Braus for Spinax niger (11), p. 620, and by myself for Mustehis lcevis((12\ p. 347).

(2.) The number of post-girdle nerves is greater in younger embryos than in older embryos or adults (cf. Table III).

(3.) The last two or three post-girdle nerves form a posterior collector (cf. (12), p. 347, and (11), p. 566), a structure which is quite separate from the " Langsstamme " occurring in the adults. These latter structures also are found in embryos of 42 mm. and upwards. In the two younger embryos (A and B) they are not yet fully formed (cf. fig. 7). I have only observed a posterior collector in one case among older embryos and never in adults. In the older embryo in which it occurred there were eleven post-girdle nerves, and the two branches of the posterior collector were extremely fine.

(4.) There is a certain amount of variation in the number of the pelvic foramina. Asymmetry occurred in one case, C.

The fact that the fin innervation area has a greater extent both caudally and rostrally in the embryo than in the adult, offers no criterion between the rival theories. On the side fold excalation theory we