OP ARTS AND SCIENCES. 69 



above that the gills can be seen behind the operculum, or when they 

 are separated from the body in breathing (Plate II. fig. 16). Usually 

 the gill-cover is pressed closely against the sides of the body, but in 

 breathing an opening is seen (Plate IV. fig. 37) through which water 

 is constantly passing, a strong current being made by the rapid mo- 

 tion of the pectorals, against the base of which the extremity of the 

 gill-cover is closely pressed (Plate IV. fig. 42). The large yolk-bag 

 is opaque, of a bluish-gray color. The body of the young Lepidos- 

 teus is quite colorless and transparent. The embryonic fin is narrow, 

 the dorsal part commencing above the posterior end of the yolk-bag ; 

 the tail is slightly rounded, the anal opening nearer the extremity of 

 the tail than the bag. The intestine is narrow, and the embryonic fin 

 extending from the vent to the yolk-bag is quite narrow. In a some- 

 what more advanced stage (Plate I. fig. 3), — hatched a few hours 

 earlier, — the upper edge of the yolk-bag is covered with black pig- 

 ment cells, and minute black pigment cells appear on the surface of 

 the alimentary canal. There are no traces of embryonic fin-rays either 

 in this stage or the one preceding ; the structure of the embryonic fin 

 is as in bony fishes — previous to the appearance of these embryonic 

 fin-rays — finely granular. Seen in profile, the yolk-bag is ovoid ; 

 as seen from above, it is flattened (Plate I. fig. 1), rectangular in 

 front, with rounded corners, tapering to a rounded point towards the 

 posterior extremity, with re-entering sides (PL I. fig. 7). 



The head seen from above is rounded anteriorly, fringed by the row of 

 suckers which form a connected, thickened margin ; the eyes scarcely 

 project beyond the general outline of the head ; the gill-covers are small 

 lobes immediately behind the eyes. The brain occupies but a com- 

 paratively small part of the head; the olfactory lobes are greatly 

 developed, and elongated much as in Sharks and Skates, the posterior 

 extremity of the brain rising obliquely towards the back and leaving 

 a considerable distance between the base of the brain and the 

 termination of the chorda, which ends between the otoliths (Plate I. 

 figs. 6-11). 



The second day after hatching, we can detect (Plate I. fig. 11) 

 the first trace of an upward curve to the extremity of the tail. Up 

 to this time, the chorda is straight, as is the embryo of any newly 

 hatched bony fish ; the yolk-bag has also greatly decreased in size ; 

 the head makes a less sharp angle with the longitudinal axis ; the 

 snout formed by the sucking-disk projects well beyond the outline of 

 the opening of the mouth ; the gill-opening is heart-shaped, and the 

 heart can distinctly be seen to beat at the junction of the yolk-bag 



