288 Proceedings of the Royal Society of Victoria, 



ff. 



///.* J£\ 



iv 



Fig. 5 shows the following positions of the nerves in the forms 

 i. to iv. In form i., nerve IV. is clistincly free from nerve III. ; 

 in form ii. a branch passes between the two nerves, either from 

 nerve III. to IV., or vice versa; in form iii. we find a still closer 

 connection, III. fusing with IV. at one point, while in form iv. 

 the fusion is continued for some distance. But since we found 

 that nerve III. agreed in its manner of increase with that in 

 Bnfo variabilis and Pelobates fuscus, it will be most instructive to 

 take its evidence into consideration. 



In Table N then the most primitive form should occur most 

 frequently with the smaller thickness and the most advanced 

 with the higher thickness of nerve III., and according to this 

 table we find that form i., which Table M shows to be the most 

 primitive, occurs chiefly with a lower thickness than does form 

 iv. the most advanced, which so far confirms the previous results. 

 Form iii. shows a slight irregularity in thickness 15, which may 

 possibly be due to the small number of observations in that 

 thickness. It seems therefore that in Hyla aurea, as nerve IV. 

 increases in thickness, advancing in development, it takes an 

 increasing share in the formation of the brachial plexus. 



