Two abnormal Plutei of Echinus, and the light which they throw on the Factors in the normal development of Echinus

The present paper deals with two remarkable larvæ, the first a larva of Echinus miliaris obtained in a culture reared from eggs fertilised in the Zoological Laboratory of the Imperial College of Science and Technology, and the second a larva of Echinus esculentus obtained in a culture of eggs fertilised in the Laboratory of the Marine Biological Station at Plymouth. The second and more interesting specimen I owe to the kindness of Mr. de Morgan, by whom the culture in which it appeared was instituted.