1890.] MICROSCOPICAL JOURNAL. 93 



made a special study of the life of fishes. By way of introduction he 

 mentioned how the color of fishes varied under different conditions : 

 the color of the food would modify it, or the color of the bottom of the 

 sea where the individual made its habitat would change it. The same 

 species, under these varying conditions, would show a marked differ- 

 ence of color in tide pools separated but a few feet. In this latitude 

 most fishes frequenting our shores and coming near the surface are a 

 dove color. The species found at a depth of 200 fathoms or more are 

 plain black or plain white. Farther south they assumed a brighter hue. 

 Professor Alexander Agassiz obtained different colors in the same fish 

 by changing its surroundings, or by placing it over sand of difierent 

 colors. 



In order to fully explain the formation of the chromatophores or 

 color cells, the speaker gave a brief outline of the development of the 

 fish, its embryology. A number of carefully made drawings supple- 

 mented various preparations shown under the microscope, and the va- 

 rious stages of the embryro were drawn on the black-board. The 

 pelagic ova, being lighter than the sea water, float to the surface and 

 there pass rapidly through the various stages in the embryonic state. 

 Most of the observations noted were made in the vicinity of San Diego, 

 and were confined to the ova obtainable in or near the harbor, as he 

 had nothing but a row-boat in which to make his excursions, and it was 

 not possible to go long distances, gather and convey them to his labor- 

 atory and note the rapid changes. 



Rider first called attention to the origin of color. At fourteen hours, 

 he says, the embryo begins to show signs of the development of the 

 pigment just below the superficial layers of the epiblast. These cells 

 are at first scattered irregularly over the body of the embryo, and grad- 

 ually grow darker. As they do this they also become irregular in form 

 and flattened, with a number of points running out from them. Later 

 they tend to aggregate on certain parts of the body. The rearrange- 

 ment appears to be accomplished by their migration toward definite 

 points, by means of an amaiboitl movement of their entire substance. 

 By the time the young fish is ready to hatch, the covering of the oil 

 sphere is found to be more or less covered with pigment, which seems 

 to have in part developed in the cellular mantle. 



Agassiz and Whitman give a more satisfactory account in describing 

 the early stages of Cottus grcenla7idicus and Motella argentea. Of 

 the first they say the pigment is at first extremely pale, and confined to 

 a few mesoblastic cells along each side of the embyro. In the course 

 of an hour the number of young pigment cells is much increased, and 

 a few black pigment dots make their appearance. By this time some 

 of the pigment cells of both colors have wandered away from the lat- 

 eral mesoblastic masses of the embryo, and appear as isolated amaeboid 

 cells, between the ectoderm and the layer which we have called the 

 periblast. In Motella^ pigment cells first appear near the closing of 

 the blastopore, and they are developed along the sides of the embryo 

 from the blastopore forward. 



Pigment is nearly always found sometime before hatching, and as the 

 embryonic life is usually short, lasting from eighteen to forty-eight 

 hours, and the eggs are transparent, the whole process, from fertiliza- 

 tion to hatching, can be observed without any very great inconvenience. 



