1895.] SENSOBY CANAL SYSTEM OF FISHES. 287 



sides of the walls of each cavity there arise a series of sensory 

 filaments (PL XIX. figs. 8 and 9) into which a fine branch of a nerve 

 passes. In ScMsmatorhynchus Jieterorhynchus, Leydig (8. p. 2) 

 describes the walls as showing folds as figui-ed (Taf. i. fig. 5). In 

 Labeo these folds were scarcely discernible, probably owing to the 

 fact that the material had been for some time in alcohol. 



These interesting organs seem to me to be a series of specialized 

 cluster-pores which have become isolated from the sensory canal 

 system. There are a number of other " sense-papillae," as Leydig 

 terms them, common to certain Cijirrinidw, which have also 

 probably originated as cluster-pores. 



IV. EsociDiE. 



ESOX LTJCITJS. 



General Description. 



The sensory canal system of Esox has been previously investi- 

 gated or referred to by Leydig (7), M'Donnell (9), Eamsay Wright 

 (12), Allis (1), and others. 



The system is a simple one and shows none of the complications 

 previously met with in the Siluroids or Cyprinoids. 



The lateral canal, like all the canals in Esox, is a wide tube 

 passing from the posterior end of the body to the anterior, and 

 joins the main canal of the head by passing through tlie supra- 

 clavicle and a somewhat Y-shaped canal-bone; the lateral arm 

 connects the lateral canal of the trunk ^vith the main canal of the 

 head, which passes through the lateral border of the pterotic, and 

 on the sphenotic divides into supra- and suborbital branches. The 

 former passes through the frontal to a point sUghtly anterior to 

 the lateral ethmoid, and then into a canal-bone lying on the lateral 

 border of the anterior portion of the frontal. It terminates 

 anterior to the nasal capsule some distance from the end of the 

 snout. The suborbital passes over the sphenotic in a small ovoid 

 canal-bone and is conducted around the orbit in a series of canal- 

 bones. In front of the orbit it makes an upward turn and ter- 

 minates at a pore lateral to the nasal capsule. 



Passing through the preoperculum is a fairly large canal, which 

 has no connection with the main canal or with that in the 

 mandible. This last mentioned commences on the ventral surface 

 of the mandible a little anterior to the articular portion, and passes 

 to almost the end of the ramus. It is not connected with the 

 branch of the opposite side. 



In addition to the above canals and branches there are in Esox 

 a number of open grooves upon the surface of the head posterior 

 to the occipital region and in the nasal region. 



Gimrse of the Canals and Branches. 



1. The LateeaIi Cajtai,. — The presence of a canal on the lateral 

 trunk of the body seems to have escaped the notice of previous 



