430 ZOOLOGY. 
the middle of May and the 8th of June, remaining at other 
times of the year in deep water. 
The young begin to hatch about the end of May. At 
first the embryo gar possesses an unusually large yolk-sac, 
while the notochord is very large; otherwise posteriorly it 
resembles the young of bony fishes. It differs, however, in 
its large mouth, which is surmounted with a hoof-shaped 
depression edged with a row of projecting suckers, by which 
it attaches itself, hanging immovable, to stones; the eye and 
brain is smaller than in bony fishes. The tail is at first 
protocercal, beginning on the second day to become hetero- 
cercal. On the third day the gill-covers form rectangular 
flaps, and the first traces of the pectoral fins appear, while 
the snout becomes longer. By the fifth day the traces of 
the dorsal, caudal, and anal fins appear. When a little over 
three weeks old it assumes a more fish-like form ; the suck- 
ing disk has nearly disappeared, the lower jaw greatly length- 
ened, and the gill-covers extend to the base of the pectoral 
fins. When between two and three weeks old the young 
gar-fish is 20 millimetres (?inch) long. The young rise to the 
surface to swallow air, as in the adult. Soon after this it is 
of the form first discovered and figured by Wilder. The 
gar-fish, according to Agassiz, bears some resemblance to 
the sturgeon in certain stages of growth, and in the forma- 
tion of the pectoral fins from a lateral fold, as well as by the 
‘mode of growth of the gill-openings and thegill-arches, while 
it closely resembles the young of bony fishes in the develop- 
ment of the posterior part of the body, by the mode of origin 
of unpaired fins from the embryonic fin-fold, and by the 
mode of formation of the fin-rays, and of the ventral 
fins. 
The mud-fish, Amia calva Linn., is like an ordinary bony 
fish in form, with rounded scales; the caudal fin ‘‘ masked 
heterocercal,” the snout is short and rounded, and the air- 
bladder is large and cellular. It attains a length of two 
thirds of a metre, and occurs in the Mississippi Valley and 
as far east as New York. A fossil form closely allied to 
Amia dates back to the Cretaceous Age, and the genus 
Caturus is a Liassic and Oolitic genus. 
