Quantitative studies of variabilities and of nutrient partition between cerebral hemispheres, optic lobes, cerebella and bodies of individual chick embryos.

The extent of variability in weight, DNA content and protein content of cerebral hemispheres, optic lobes and cerebella of individual brains has been studied in newly hatched chicks in which these parts can be easily delineated and quantitatively dissected out. The variabilities were within narrow ranges; nevertheless, for some individuals the above parameters were significantly higher. Correlations between such parameter values for egg and body weights, and different brain parts of the same animals were also studied. Body weights were significantly correlated with egg weights. Cerebellar weights were significantly correlated with both egg weights and body weights, but cerebral hemispheres weights and optic lobes weights were not. Thus, larger body necessitates larger cerebellum, and this variability appears to be environmental (amount of egg nutrients) rather than genetic. On the other hand, in the chick larger body does not necessitate larger cerebral hemispheres and larger optic lobes.