Inhibition of Pigment-Cell Migration in Triturus torosus

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Abstract
Individual counts on 64 individuals in azide and 79 controls, and 130 individuals in cyanide with 123 controls show that numbers of melanoblasts which migrate ventrally from the neural crest and become visible on the sides of the body between the base of the gills and the anal level are decreased by exposure to Na azide and KCN from developmental stages before migration has begun or before it has progressed far. Individual averages vary widely, according to concn. of the agents, differences in individual susceptibility and probably other factors. Expressed as percentages of control averages, the cells adjoining the yolk border (A-cells) range from 12.9 in the highest azide concn. to 75.7 in the lowest cyanide concn. Individual averages for all visible migratory cells (AB-cells) were detd. only for the lower azide concns. used. Expressed as percentages of control averages, they range from 47 to 64.8. For all cyanide concns. used, they range from 34.3 to 81.3% of control averages. Cells which become visible only part way down to the yolk (B-cells) are relatively few in number but may be more numerous under the inhibiting conditions than in controls, particularly in cyanide, where they range up to 258.1% of control averages. Various lines of evidence discussed in the text indicate that the decreases in numbers of visible pigment cells in the region where counts were made are due at least in part, to inhibition of migration rather than merely to delay or prevention of pigment formation in some cells, which consequently remain invisible. The origin of the melanoblasts from the extreme high end of the dorsiven-tral gradient, the probable high activity of the migratory stage, and the almost complete absence of any other effects of the agents on development, except retardation, all favor the conclu- sion that these cells are highly susceptible to the inhibiting conditions and that this susceptibility is related to the gradient pattern of the embryo and larva. Individual counts of right and left sides separately serve as examples of variations in numbers of cells on the 2 sides of the individual and in different individuals. Recounts in the agents and after 8 days in water following exposure to cyanide show no distinct increases in cell numbers and indicate that the first counts were fairly accurate.

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