142 Edward Phelps AUis jr., 



organ usually so enclosed; while the 2"^^ was never entirely enclosed. 

 The imperfect bridges of bone were however always completed by a 

 dense connective tissue which closely envelops the entire bone as if 

 it were a highly developed periosteal membrane. Between the bridges 

 of bone or tissue that thus enclose these several organs there are 

 open bays in the bony canal, each bay lodging the base of a mem- 

 branous pouch which represents one of the primary tubes of the line. 

 Two of these pouches thus take their origin from the canal as it 

 traverses the lachrymal, each of them opening on the outer surface 

 of the head by a single pore, these pores being the 3^'<^ and 4*^ ones 

 of the line. The anterior and posterior edges of the lachrymal, where 

 the canal enters and leaves it, are both fringed with flbro-cartilage. 



Posterior to the lachrymal the canal, as it encircles the ventral 

 and posterior margins of the eye, traverses four fibro-cartilaginous 

 tubes, each of which is partly ossified and lodges a sense organ in its 

 ossified portion. The first one of these four tubes is considerably 

 longer than either of the others and is suborbital in position. The 

 other three are postorbital in position, the most dorsal one occupying 

 the position, in its relations to the canal, of the postfrontal bone of 

 Amia. Between each two consecutive tubes, between the first tube 

 and the lachrymal, and also dorsal to the last tube, there is a mem- 

 branous pouch, the five pouches representing the 5*^ to the 9*^ 

 primary tubes of the line. The 5*^ and 6*^ pouches open by single 

 pores on the outer surface of the head. The other three pouches were 

 blind in all my adult specimens, and also in the two young specimens 

 examined by sections. 



These several pouches, representing the 2^^ to the 9*^ primary 

 tubes of the line, all open into the canal by relatively large openings, 

 certain of these openings being so large that the pouches might be 

 described as swellings of the canal, as CoUinge has described them, 

 though in reality they are swellings of the primary tubes and not of 

 the canal. The 3^'^ and 4^^^ pores of the line are the surface openings 

 of the first two pouches. They lie at or near the upper edge of the 

 maxillary furrow, opposite its deepest part, the 4*^^ pore being usually 

 entirely enclosed in the furrow, and hence not visible on the outer 



