656 BASHFOKD DEAN, 



Teeth take their origin at the bottom of deep tube-like insinkings of 

 the mucosum: these are implanted irregularly in the dentigerous 

 regions, without any apparent attempt at the production of a general 

 dental trench. The pharynx of the early stages, PL 9, Figs. 1—8, 

 is a well marked cavity although its dorsal and ventral walls are 

 closely apposed ; in the gullet the lumen is wanting, a secondary con- 

 dition known to be of very general occurrence among fishes since 

 the tirae of the studies of Balfour. The reopening of the gullet 

 takes place at about the stage of PI. 9, Fig. 10. And at nearly the 

 sarae time the swim-bladder takes its origin as a crease-like in- 

 vagination of its dorsal wall; its rapid growth has by the stage of 

 PI. 10, Fig. 19, given it the following characters: anteriorly, in the 

 transverse plane of the opercules a narrow dorsal longitudinal slit, 

 Fig. A ; in the plane of the bases of the pectorals the swim-bladder's 

 dorsal wall becomes enlarged, bilobed, although still retaining its 

 opening to the gullet, Fig. ß ; in a plane immediately hindward of 

 the tips of the pectorals it has become distinctly tubulär. At the 

 stage of PI. 11, Fig. 22, the swim-bladder has assumed the following 

 characters : in the transverse plane corresponding with that of Fig. A, 

 its opening into the gullet is slit-like, its neighbouring mucous walls 

 notably convoluted, Fig. D; shortly behind this position, in a plane 

 still passing through the opercula, Fig. E, the swim-bladder is a large 

 thin and smooth walled Chamber, attached to the dorsal wall of the 

 anterior portion of the stomach by connective tissue but otherwise 

 unconnected with it ; this attached condition the swim-bladder maintains 

 as it passes down the mid-dorsal region of the visceral cavity, its 

 diameter first increasing then diminishing tili it terminates slightly in 

 advance of the plane of the ventral fins. In its hinder region, Fig. F, 

 it is somewhat deeper than wide, with thicker vascular walls. In 

 this stage the adult conditions have practically been attained. 



b) Anus, po st -anal gut, neu r enteric canal, hinder 



region of excretory ducts. 

 In Teleosts generally the anus is formed at a reraarkably early 

 period, — in Serranus (H. V. Wilson) before hatching. In the 

 Ganoids its formation is later, at about the same time as the mouth 

 opening, — in Ämia at about the bcginning of the second day. In 

 Teleosts the abbreviation of the process is probably the cause of the 

 formation of the anus directly, i. e., without proctodaeum; in Ämia, 

 on the other band, a proctodaeum, although small, unquestionably oc- 



