232 CLAPP. [Vol. XV. 



quite noticeable in Batrachus, as also the numerous " surface 

 sense organs " (terminal buds) described by AUis (2) on the 

 head of Amia. 



Variations. 



Frequent variations in the number and position of the organs 

 have been noted. There may be five, six, or seven organs in 

 the antorbital portion of the infraorbital line. The number 

 in the suborbital may be eight or nine. In the mandibular 

 line at the place of union of the opercular and mandibular 

 divisions one organ is often wanting. 



Two extra organs — one on each side of the head — 

 occurred in the case of one specimen, confirming the opinion 

 that the free organs of this region are homologous with those 

 of the commissural canal in the occipital region of Amia. 

 (Compare Figs. 21 and 22.) 



On the body the variation is still more marked, the two sides 

 seldom having exactly the same number or arrangement of 

 organs. 



On one large specimen there was the following arrangement : 



In the dorsal body line of the right side, 25, left 29. 

 " " middle " " " " " " 11, " 8. 

 " " ventral " " " " " " 26, " 27. 



At the anterior end of the ventral line in another specimen 

 one organ was lacking on each side. The number may be four, 

 five, or six on the caudal fin. 



Innervation. 



The method most successfully employed for determining the 

 course of the nerves was maceration of the adult fish in nitric 

 acid. After being kept for some time in a weak solution, not 

 only the large nerve trunks could be easily followed, but the 

 bundles composing these trunks could be separated, the con- 

 nective tissue sheath having been dissolved. It thus became 

 possible to demonstrate the course of the different components 

 of nerves enclosed in the same sheath. 



