On Relative Growth in Pinnotheres pisum

SUMMARY.1  The abdomen of the female Pea‐Crab Pinnotheres yisum shows an extremely high growth‐rate relative to that of the carapace, especially in early stages measured. That of the male shows very slight positive allometry. 2  There is a very shallow growth‐gradient in the male abdomen with its centre in segments V, VI. In the female the gradient is at first very steep with its centre further back, between segment VI and the telson. 3  The relative growth of each segment of the female abdomen shows three successive periods of simple allometry with a progressively lower relative growth‐rate. 4  In the second period the fall in growth‐rate is less marked in the telson than in the segments immediately in front. Finally, in the third period a definite centre of low growth‐rate appears in segment VI, where originally it was highest, the growth‐rate increasing both forwards and backwards. This encourages speculations concerning the control of growth by a centre of inhibition.“ 5  Direct plotting of the data gives a somewhat simpler picture of growth, though careful scrutiny of the relative goodness of fit indicates that the logarithmic plotting gives a better representation of growth. This may mean that growth is determined intrinsically in the tissues themselves rather than by a general supply of “growth‐factor” from the body. 6  An analogy is offered to the distal movement of the growth‐centre and steepness of the gradient when relative growth of the whole organ becomes very high. 7  Growth during this period is largely by increase in cell‐number rather than by increase in cell‐size.