DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 903 



increase both in number and size at the sixth week, large recurved teeth appearing on 

 the hyoid, while the pharyngeal cartilages are similarly studded. 



Both wolf-fish and salmon, on hatching, are, however, devoid of teeth ; but develop- 

 mental changes seem to be more rapid in the latter than in the former, the cartilages appa- 

 rently being more actively plastic, and the advanced stage at which exclusion from the egg 

 takes place afford greater time for maturity. Thus at the seventh day Meckel's cartilages 

 are separated by a cellular band in front, while they are less rounded than in Anarrhichas. 

 A short distance behind is a line marking off the articular piece. Four teeth are visible, 

 symmetrically placed and developed from the mucous membrane in the usual manner. 

 The first presents a glassy coat of ossific matter, forming the point and sides ; beneath 

 this a narrow layer of dentine occurs, while the centre contains the cellulo-granular 

 pulp continuous with the oral mucous membrane. It is placed behind the symphysis, 

 and is slightly inclined backward ; the second is larger and stronger, with a more decided 

 backward curve, while the third is a straight tooth about the size of the first ; the fourth 

 is similar, but shorter. In the upper jaw are ten teeth ; but all that can be said is that 

 four lay in proximity to the maxillae, two (vomerine ?) intermediate, and two at a greater 

 distance. 



Pleuronectes Jlesus, when j^ i ncn ' m length, has numerous teeth in both the upper and 

 lower jaws. They pierce the oral mucous membrane as acutely pointed hyaline structures ; 

 the mandibular cartilage at this time being completely encased in hyaline tissue, and 

 sending down from its inner ventral margin a sharp crest of the same hard substance, 

 whi]e the teeth occupy a corresponding position on the inner margin superiorly, and have 

 their points directed inward. Numerous papillae with developing teeth also occur. The 

 pharyngeal teeth in the post-larval goby, -^ inch in length, and in Labrus, T 7 ¥ inch long, 

 show interesting stages of growth. In the former species, on both the floor and roof of 

 the pharynx, the dental sacs are crowded together ; but in Labrus they extend along the 

 under surface of the basi-branchial plate, as well as on the pharyngeal floor. Each tooth- 

 sac is formed of deep columnar cells, in which the conical tooth is seated on an internal 

 cellular pulp or papilla. The tooth is formed as a hard hyaline cap — semilunar in 

 transverse section — which becomes more conical, and finally, when very acuminate, pierces 

 both the sac and the epithelium of the pharynx. At the tip the tooth is solid, and a 

 little below a neck or ring of clear deeply-stained tissue exists, the hollow portion or 

 root of the tooth beginning at that point. Some of the teeth appear to be compound, 

 and give off one or more denticles from a common papilla enclosed in hyaline tissue ; 

 while in other cases separate teeth occur, in such close proximity that three or more may 

 be present in a single fold of the pharyngeal epithelium. The teeth may lie deep in the 

 pharyngeal wall; indeed, some of these structures in a young post-larval Labrus are 

 separated from the pericardial chamber underneath merely by the thin pericardial layer, 

 and in this species the subepithelial tissue of the pharynx is in some parts little else 

 than a mass of tooth-sacs. In the post-larval gurnard, ^ inch in length, the cartilaginous 

 mandible is completely surrounded by hyaline tissue, and in some of the microscopic 



