Postembryonic growth of the optic lobe of Octopus vulgaris, Lam.

Abstract

AbstractThe pattern of growth of the optic lobe of Octopus vulgaris has been investigated from 0.1 to 6.0 gms body weight by measuring the weight of the lobe and the number of nuclei present in the tissue homogenate. In the normal habitat, the rate of increase in nulcear number relative to increase in body weight is 1.32 up to 1.5–1.8 gms, but undergoes a three‐fold decrease above this size. On the other hand, the rate of increase in tissue weight remains essetially constant throughout the same period of development, with the exception of the interval between 1.0 g and 1.5 gms during which it rises markedly. Nuclear density increases steadily up to approximately 1.2 gms and approaches a constant value above this size.In octopuses reared in transparent containers or under an opaque cover the rates of increment in number of nuclei and in tissue weight are generally lower than normal between 0.2 g and 1.5 gms. In both experimental conditions the wave of acceleration in the rate of increase of tissue weight occurring between 1.0 g and 1.5 gms in normal animals appears earlier particularly in octopuses reared under an opaque cover. At body weights larger than 1.5–2.0 gms the rates of increment in number of nuclei and tissue weight become higher than normal in octopuses reared in transparent boxes, but change in the opposite direction when rearing takes place in opaque containers. In the former condition, the nuclear density of newly added tissue starts decreasing earlier than normal but reaches a higher level at body weights above 2 gms, while in octopuses reared under an opaque cover the decrease occurs at approximately normal timing but attains lower values at higher body weights.