Vol. VI. JULY, 1889. No. 45 



CONTRIBUTION FROM THE SAN DIEGO BIO LOG. 

 ICAL LABOR A TOR Y—IL 



ON THE GENESIS OF THE COLOR-CELLS OF EISHES. 



So far as I am aware the origin of the color-cells or chromato- 

 phores of fishes has never been discussed. A. Agassiz (on the 

 Young Stages of Bony Fishes, ii) has described the color changes 

 of young founders, and Agassiz and Whitman have promised a 

 discussion of the genesis of the chromatophores in the second 

 part of their paper on "The Pelagic Stages of Osseous Fishes" 

 which has not yet appeared. 



My observations have been based on the embryos of many 

 species, but for the present purpose only those of Sciaena sat- 

 urna, Hypsopsetta guttulata and Pleuronichthys coenosus (?) are 

 available. Naturally the genus Stolephorus and many other 

 Isospondylous fishes in which no color is observed forty-eight 

 hours after hatching, are not available for a study of the origin of 

 the color-cells; nor can any use be made of such genera as Oligo- 

 cottus, Isesthes, Atherinops and Atherinop^is, in which the color 

 appears in the egg after several days, and then appears at some- 

 times widely separate portions of the embryo. 



The eggs of Hypsopsetta and Sciaena may always be collected 

 in greater or less abundance in San Diego Bay during the latter 

 part of April, the whole of May, and at least a part of June. The 

 eggs are deposited at about five o'clock in the evening. They 

 are pelagic; the only difference between the eggs of the two 

 species seems to lie in the slight difference in size and in the num- 

 ber of oil-globules, Hypsopsetta invariably having one, Sciaena 

 from two to eight. 



The eggs were carried a mile before they could be studied, so 

 that, in the earliest stage observed the blastodisk was segmented 

 into four cells. The embryonic ring and shield appear in about 

 twelve hours; the blastopore closes in about eighteen hours; the 

 embryos are freed from the membrane in less than thirty-six 

 hours. At the closing of the blastopore, the embryo and a part 

 of the yolk are covered with scattered chromatophores. At this 

 time the individual chromatophore is a large cell with a distinct 

 nucleus and a few color granules; there may be present one or 



