The Latero-Sensory Canals and Related Bones in Fishes. 



Edward Phelps Alii s jr. 



With plates VIII— XX. 



There is still considerable question as to the value of the lateral, 

 or more properly latero-sensory, canals of fishes for the determination 

 of tlie homologies of the cranial bones. Perhaps the strongest and 

 most frequently quoted evidence against their value has been Sage- 

 mehl's statement that in the Characinidae and Cyprinidae, the supra- 

 temporal canal traverses the parietal bone, instead of traversing, as 

 in Amia, Polypterus, and many teleosts, a transverse extrascapular 

 bone or bones. Sagemehl's explanation of this supposed fact was that, 

 because of this radical difference in its position, the canal in the Cha- 

 racinidae and Cyprinidae could not be the homologue of the canal in 

 the other fishes mentioned. This had also always been my own opi- 

 nion, but Dr. G. A. Boulenger. of the Natural History Department 

 of the British Museum, having kindly sent me a specimen each of 

 Macrodon, Alestes and Hydrocyon, an examination of these three spe- 

 cimens at once convinced me that it is the parietal bones of these 

 fishes, and not their supratemporal canals, that are not the homologues 

 of those in the other fishes referred to. This conclusion having a 

 direct and important bearing on the general question of the value 

 of the lateral canals for the determination of the homologies of the 

 related cranial bones, and this being an ever-recurring question in my 

 work, I have been led to look up the literature of the subject as 



Internationale Monatsschrift für Anat. u. Phys. XXI. 26 



