The Problem.

My recent research has been concerned with elucidating three principal questions. These are:—

• (1) What is the true nature of the development of Amphipholis squamata, and, in particular, what is the mode of origin of the coelom in the species?'

• (2) To what extent has viviparity affected development, and in what ways has it done so?

• (3) What are the causes of direct development in ophiuroids, and how have they acted?

This paper is concerned only with the first of these problems, namely, elucidating the real mode of development of Amphipholis squamata. The second and third questions are considered in a separate paper (Fell, 1945) in which are utilised some of the results given here.