228 BULLETIN OF THE UXITED STATES FISH COMMISSION. 



gitudinal folds. The first of the unpaired fins to bo developed was the 

 anterior dorsal, which was first marked off from the rest of the natatory 

 fold on the fifth day by a slight emargination near the anterior end of 



the latter. Coinridently with the development of the first dorsal the first 

 rays of the caudal began to develop on the fifth day, just below the up- 

 turned caudal end of the notochord, which terminated near the dorsal 

 border of the tail, but no distinct embryonic caudal lobe was ever devel- 

 oped such as that described by A. Agassiz in the young of Plewronectes. 

 The development of the tail was iu fact very similar to that of the 

 salmon, even to the presence of a similar vascular plexus and a 

 small but perceptible venous sinus. On the seventh day the meso- 

 blast was perceptible in the anterior dorsal and in the anal, and 

 the rays in these two fins had begun to develop. On the seventh day 

 the caudal had assumed a clearly-marked fan shape. On the eighth day 

 the anal was more apparent as a prominent expansion of a part of the 

 ventral portion of the natatory fold, and its rays had become more dis- 

 tinctly visibl e. By the tenth day the rays in the first dorsal and the 

 anal were distinctly developed, and both fins were sharply marked off 

 from the rest of the fins developed from the natatory fold by deep 

 angular emarginations. On the tenth day the adipose dorsal appeared as 

 a separate lobe, which became progressively more distinctly developed. 

 On the eighth day the ventrals budded out as a pair of folds above the 

 hinder end of the yelk sack, at the lower edge of the body, just a little 

 way in front of the vent. On the tenth day the caudal became distinctly 

 lobed and posteriorly emarginated, the upper lobe being the longest, 

 and on the eleventh day all of its rays were defined. By the thirteenth 

 day the yelk had been absorbed, and the young fish were nearly ready 

 to feed. By this time, too, the rays had appeared in the ventrals. By 

 the fourteenth day the first hard spine of the anterior dorsal was de- 

 veloped, and the anterior spiny rays of the pectorals had been formed 

 with two retrorse hooks on their hinder margins. By this time the 

 young had practically passed through their larval condition, and began 

 to bear a striking similarity to the adults, having by this time also be- 

 come quite dark on the upper side of the body from the development 

 of pigment cells in the skin. 



On the fifteenth day after oviposition it was found that they would 

 feed. While debating what should be provided for them, Mr. J. E. 

 Brown threw some pieces of fresh liver into the aquarium, which they 

 devoured with avidity. It was now evident that they were provided 

 with teeth, as they would pull and tug at the fragments of liver with 

 the most dogged perseverance and apparent ferocity. Tins experiment 

 showed that the right kind of food had beeu supplied, and as they have 

 up to this time (August 1) been fed upon nothing else, without our 

 losing a single one of the brood, nothing more seems to be required 

 with which to feed them. 



