of the, Pelvic Plexus in Acanthias vulgaris. 



17 



On the migration theory, we should expect to find the more rostral 

 position of the girdle associated with a lessened number of collector- 

 nerves. The reduction of the collector nerves, however, does not 

 keep pace with the more rostral position of the girdle. Erom fig. 6 

 we see that with a change of five segments in the position of the 

 girdle, there is associated a change of only two segments in the 

 collector area. To explain this, we must suppose that those segments 

 which lie just rostral to the collector area in the case where the girdle 

 is more caudally situated, are capable of taking part in the collector 

 when the girdle is shifted more caudally. Evidence in favour of 

 such a view will be given later, when it is shown that in young 

 embryos, the number of nerves forming the collector is greater than in 

 the case of the adults (vide p. 19). 



B. Correlation between the First Girdle-piercing Nerve and the Post-girdle 



Nerves. 



It has already been seen (Table III) that on the average, the 

 number of post-girdle nerves is considerably greater in the male than 

 in the female. Consequently it has been found necessary to consider 

 the two sexes apart on this point. The way in which the number 

 of post-girdle nerves varies with the position of the girdle is shown 

 in the following two tables : 



Table XI. 



Table XII. 



VOL. LXIX. 



