LATERAL CANAL SYSTEM OF SELACHIANS 17 



can often be brought out by counterstaining on the sUde with 

 Delafield's haematoxyhn. 



Sections were cut five to fifteen micra and mounted in the 

 usual manner, avoiding, however, solutions not absolutely free 

 from acid. 



Terminology. The sense organs of the canal system are dis- 

 tributed in definite lines on the head and trunk of fishes and of 

 amphibians in their aquatic stages. While usually enclosed in 

 a canal, they are sometimes exposed on the surface or in shallow 

 grooves. The lines may be muHiple as is common in amphibia 

 and they may reach the number of nine (Herrick). 



The terminology employed in this paper is that in common 

 use with the addition of a few terms that conduce to clearness. 



The entire system of sense-organs often designated the lateral 

 line system will be called the sensory canal system. This will 

 include all of the canals of the head and the trunk and the sur- 

 face or pit-organs which are genetically equivalent to the sen- 

 sory canal organs. As before mentioned, no account is taken 

 of the vesicles of Savi and the ampullae of Lorenzini. 



The trunk canal will be called the lateral canal; the head 

 canals will l:)e designated supraorbital, infraorbital, and hyoman- 

 dibular canals, respectively (figs. 1, 2, 3). The canal running 

 over the temporal region and joining the two lateral canals 

 will be called the supratemporal commissure (figs. 1, 2). Two 

 short detached canals on the lower jaw will be called mandibular 

 canals (fig. 3). 



The term sensory canal will be used to denote any of the deli- 

 cate epithelial tubes, one wall of which is developed into the 

 line of sense-organs, sensory epithelium, or sensory column 

 (figs. 4, 5). The numerous channels connecting the sensory 

 canals with the exterior will be called tubules and their open- 

 ings on the surface, pores (figs. 4, 6). 



With reference to the nerves supplying the sensory canal 

 system, the generally adopted nomenclature will be employed 

 except in the case of the nerve supplying the lateral canal. 

 This will be called simply the nervus lateralis instead of ramus 

 lineae lateralis X. The branches of the N. lateralis which .supply 



THE JOl'RXAI. OF COMPARATIVE NEUROLOGY, VOL. 28, NO. 1 



