ABSTRACT
According to Minot (1908) the amount of new tissue formed per gram of mammalian embryo per unit time falls with decreasing velocity as the embryo gets older, so that for very young embryos this specific growth-rate is astonishingly high, whilst the decrease in its value is not in any obvious way associated with a scarcity of the raw materials for growth. How far such an inherent decline characterises the specific growth-rate of a cold blooded animal is entirely unknown. Within more recent years, Robertson (1923) has suggested that the growing period of an animal’s life can be resolved into one or more independent cycles and during each of these cycles the growth-rate is controlled by two factors. One of these factors is always proportional to the size of the organism, and therefore constantly increases; the other factor is a linear function of the size of the organism, but decreases as the animal grows, so that the rate of growth (δx/δt) is proportional to x (a − x) where x is the weight of the organism and a is a constant representing the maximum weight reached by the animal at the end of a particular phase of growth. If this be so, it follows that the growth-rate must reach a maximum when the animal is half grown.
The rate of oxygen consumption per gram of embryo is constant from 40th–7oth day of incubation at 10°, after which it declines under the particular conditions which existed during the measurements (Gray, 1926).
If 
then z reaches a maximum value when 
. In equation (vi)a =6·25, b =3·81, hence x is a maximum when y =1·56 k2.
