(1) The rapid and marked increase in area of the hen's comb is proved both in adult and young hens to occur simultaneously with the periods of egg-laying.
(2) This increase of the comb in the hen is due to a fatty infiltration of the central connective-tissue core of the comb; the decrease in the comb is due to the abstraction of the fat. The cock's comb only contains small quantities of fat comparatively in the central core, the substance of the comb consisting principally of fibrous connective tissue. The cock's comb does not exhibit marked fluctuations like the hen.
(3) The increase in the comb is not accompanied by a rise in general body-weight, though such a rise usually occurs some time before the increase and fat deposition occur.
(4) The explanation of the fatty infiltration of the comb is found in the fact that at the egg-laying periods the blood becomes charged with fatty material which is conveyed to the ovary for the formation of yolk, aud that the excess of this fatty material is deposited in the comb.
(5) A close parallel is observed in the fat metabolism of the laying hen and of spider-crabs parasitised by Sacculina.