. Memoirs and proceedings of the Manchester Literary & Philosophical Society . studied, and consistof more or less concentric ridges, varying in number andthickness. From the commencement of the nepionic stage theyoung animal ploughs its way through the mud, with theresult that growth at the anterior end is hindered, sothe posterior end develops more rapidly. The unequalgrowth is more marked than in the typical Uniones,probably because the shell is far thinner throughout life inA nodon. At the end of the third year the posterior end has sogained in growth on the anterior that the originally ce
. Memoirs and proceedings of the Manchester Literary & Philosophical Society . studied, and consistof more or less concentric ridges, varying in number andthickness. From the commencement of the nepionic stage theyoung animal ploughs its way through the mud, with theresult that growth at the anterior end is hindered, sothe posterior end develops more rapidly. The unequalgrowth is more marked than in the typical Uniones,probably because the shell is far thinner throughout life inA nodon. At the end of the third year the posterior end has sogained in growth on the anterior that the originally centralposition of the umbo has been lost, the post-umbonal regionbeing longer than the pre-umbonal. Anodons, when moving through the mud under thewater, plough along with the head directed downwards, so 6 March, Morphogenesis of certain Pelccypoda. that the hinge line is inclined forwards in the naturalposition of the shell {, the hinge line, instead of beingparallel to the tangent to the ventral surface, verticallybelow the umbo, would meet it at an acute angle if pro-. 4 years. X 1 6 years A — space representing thelost wing. B = \vin<x. X I About lO years
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