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 (f 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 the gill-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. 



