<!. \XOIDE I. 



are 



\ 



There is still a continuous dorso-ventral fin, in which there 

 as yet no fin-rays, and the anterior paired fins are present. 



The yolk-sack is very 

 large, but its communication 

 with the alimentary canal is 

 confined to a narrow vitelline 

 duct, which opens into the 

 commencement of the intes- 

 tine immediately behind the 

 duct of the liver, which is 

 now a compact gland. The 

 yolk in Lepidosteus thus be- 

 haves very differently from 

 that in the Sturgeon. In the 

 first place it forms a special 

 external yolk-sack, instead of op 



an internal dilatation of part 

 of the alimentary tract ; and 

 in the second place it is placed 

 behind instead of in front of 

 the liver. 



I failed to find any trace of a pancreas. There is however, 

 opening on the dorsal side of the throat, a well-developed appendage 



FIG. GO. VENTRAL VIEW OF THE HEAD or A 

 LEPIDOSTEUS EMBRYO SHORTLY BEFORE HATCHING, 

 TO SHEW THE LARGE SUCTORIAL DISC'. 



m. mouth ; up. eye ; sd. suctorial disc. 



FIG. 67. LARVA OF LEPIDOSTEUS SHORTLY AFTER HATCHING. (After Parker.) 

 ol. olfactory pit ; op. optic vesicle ; uu r. auditory vesicle ; mb. mid-brain; sd. suc- 

 torial disc ; md. rnandibular arch ; liy. hvoid arch with operculum ; Ir. branchial 

 arches ; an. aims. 



continued backwards beyond the level of the commencement of the 

 intestine. This appendage is no doubt the air-bladder. 



In the course of the further growth of the young Lepidosteus, 

 the yolk-sack is rapidly absorbed, and has all but disappeared after 

 three weeks. A rich development of pigment early takes place ; and 

 the pigment is specially deposited on the parts of the embryonic fin 

 which will develop into the permanent fins. 



The notochord in the tail bends slightly upwards, and by the special 

 development of a caudal lobe an externally heterocercal tail like that 

 of Acipenser is established. The ventral paired fins are first visible 



V> K. II. 7 



