VII. The development of the calcareous test of echinus miliaris

Abstract This investigation was suggested to the writer by Prof. E. W. MacBride, F. R. S., who kindly provided for study a large number of young images and a slightly more advanced urchin. These had been reared by him in the summer of 1924 and preserved in absolute alcohol. All stages from small specimens of about 3 mm. in diameter (including the spines) up to the fully-grown urchin were obtained from Plymouth. The material for studying the development of the permanent skeleton in the pluteus could not be procured until the spring of 1925. Then, an abundant supply of material, representing all stages, was obtained from some splendid cultures which Prof. MacBride had succeeded in rearing. So healthy were these cultures that many metamorphosed in 24-26 days into perfectly normal images. From the same cultures, the few early stages required to complete the study of the development of the corona were also obtained. It was necessary to rear these stages in the laboratory as they were too young to rely upon material brought up in dredgings.