STRUCTURE OF ECHINOIDS, 



179 



In all the groups mentioned above, little or no interruption of 

 the growth of new coronal plates from the oculars occurs during 

 the life of the individual. Among the Spatangida?, the most 



Text-fiij. 41. 



Adoral pai-fc of ambulacrum oiTygaster semisulcatus , showing the slight 

 mfluence of tuberculation on the position of sutures. 



highly specialised of modern Echinoids, the full complement of 

 plates IS early attained, and, for the most part, subsequent growth 



