252 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



within the tip. The urinary vesicle is distinct. The notochord is multicolumnar. The 

 surface of the yolk-sac, the pectorals, and the marginal lin arc minutely vesicular. A 

 little black pigment appears in the eye. The healthy larva' arc active. 



Next day (May 31) the chief feature was the increase in the greenish yellow hue 

 on the under surface of the head, on the yolk sac, and the tip of the tail, this hue 

 being due to the development of the cutaneous vesicles formerly mentioned, and it 

 makes a bold contrast with the pinkish oil-globule. The ramifications of the black 

 chroma topliores have everywhere increased, those at the tip of the tail having a 

 radiate arrangement like tin-rays. The liver appears on the ventral border of the 

 gut, while the rectum has moved downward a little and often contains a round mass. 

 The pectorals and otocysts are larger. In one a peculiar abnormity occurred, viz, the 

 presence of a long narrow process — resembling a diverticulum — in the rectum, which 

 in this instance had reached the somewhat defective border of the I'm. 



The changes which were visible on June 1 consisted of the projection of the 

 cartilages of the mandible, increase of pigment in the eyes, and the passage of the 

 rectum, with the urinary vesicle near the fin-margin. The little fishes are restless, 

 and the use of the pectorals in balancing is more evident. The yolk has consider- 

 ably diminished. Next day the eyes showed a greenish silvery luster, and peristaltic 

 movements occurred in the gut. Moreover, though the mouth is still closed, spasmodic 

 movements of the mandibular region take place. As in the cod, rockling, and other 

 forms, the black chromatophores, when seen against a dark background under a lens, 

 look brownish. 



June 3 the larvae were characterized bytheir activity, and especially by the rapid 

 vibration of the pectorals. Only a small anterior portion of the yoik now remained, 

 while the reddish-brown oil-globule has been drawn forward and almost concealed 

 under the greatly increased black pigment of the upper region of the abdomen. 



About a week after hatching (June 6) the larva; swam more readily, and the mouth 

 had opened — the mandible being moved up and down with the hyoidean apparatus. 

 The yolk was almost absorbed, only a- trace of the oil-globule being visible. The 

 rectum had not yet reached the border of the marginal fin, but it was close to it aid 

 its margin was papillose. Little change had taken place in the pigment of the body, 

 but the caudal patch had spread out in a characteristically fan-shaped manner (coin- 

 cident with the development of embryonic rays in the tail) and the yellowish tint of 

 the marginal fin in the same region had somewhat increased. The caudal region 

 of the marginal tin seemed to have diminished. They are hardy larvae, and could 

 without much difficulty be reared in large numbers in a suitable inclosure. 



ON THE DEVELOPMENT OF THE SAIL-FLUKE ( ARNOGLOSSUS MEOASTOMA). 



The earlier ichthyologists do not appear to have seen a ripe sail fluke or " megrim," 

 as it is often termed by the Scottish fishermen. No information on the subject is given 

 by Parnell and Couch. Day observed that "Thompson, on October 31, at Belfast, 

 procured one which had just shed its ova, only a few mature ones remaining." Raffaele* 

 pointed out that the ovaof Amog loss us have a single oil globule, and his figure oa the 

 whole resembles the present species, except that he does not show the minute structure 

 of the zona radiata. Ilis figure of the larval Arnoglossus (tav. 4, lig. 20), however, 



Lc nova galleggiauli, etc., Mil. a. (1. Zool. Ital. zu Neap., in Bd., 1 Heft, 1888, sep. abd., p. 49. 



