250 CLAPP. [Vol. XV. 



onic extension and passes upwards intracranially to the parietal 

 bone," and from thence on to the body innervating a dorsal line 

 of sense organs. This nerve is undoubtedly homologous with 

 the R. recurrens of Batrachus, although taking a somewhat 

 different course. It receives a branch from the vagus, and in 

 this respect resembles the R. recurrens facialis of Batrachus. 



4. Ill Fierasfcr the "connecting strand" is well developed, and 

 although Emery (26) describes this structure as an "epithelial 

 canal" still the evidence is hardly conclusive from his figures. 



5. Ganoids. — As already shown, Batrachus and Amia have 

 many of the same characteristics, but in Batrachus the canals 

 are never entirely enclosed within the bones of the skull, nor 

 is the elaborate system of branching canals with their numer- 

 ous groups of pores to be found. Allis (2) has shown that the 

 trigeminus takes no part in the innervation of the canal organs 

 of Amia. The terminal buds found in such abundance on the 

 surface of the head of Amia are not present in Batrachus. 



6. Selachians. — The comparison between the lateral line of 

 Acanthias and Batrachus, which has already been made, shows 

 the differences that will probably be found to exist in the mode 

 of origin of this system in the two groups of fishes. So far as 

 the innervation is concerned, there is great similarity between 

 Batrachus and selachians. Evvart (12) has shown that the 

 lateral line organs are supplied by the dorsal branches of 

 the VII and X cranial nerves. 



7. Dipnoids.- — Pinkus (13) has shown that the commissure 

 connecting the VII and X is quite prominent in Protopterus. 

 He does not describe this nerve as connecting with the branches 

 extending on to the body, but shows its union with the vagus 

 ganglion. This commissure is undoubtedly homologous with 

 the R. recurrens facialis of Batrachus. A few of the sense 

 organs of Protopterus are enclosed in canals, but they are, for 

 the most part, on the surface of the body, as in Batrachus. 



8. Cyclost07nes. — The commissure between the VII and X 

 has been found in Petromyzon and figured by Ahlborn (33). 

 Stannius (34) speaks of the N. lateralis as "formed partly by 

 a recnrrent branch from the facialis passing around outside the 

 auditory capsule, a thing zvhich does not occur in the X. lateralis 



