Introduction.

In a previous paper a general account was given of the embryology of a New Zealand ophiuroid having absolutely direct development, lacking any vestige of a larval form, and in which the coelom arose as a result of splitting in mesenchyme (Fell, 1941). For reasons stated there, it became desirable that a reinvestigation of the embryology of Amphipholis squamata should be made. The research described in the present paper was carried out from 1939 to 1941 at the Department of Zoology in the University of Edinburgh, with the aid of a Shirtcliffe Fellowship grant from the University of New Zealand. Publication has been delayed owing to the absence on war service of the writer.

The work was carried out under the direction of Professor James Ritchie, of the University of Edinburgh, to whom I am much indebted for advice and for the fine facilities of his department. To Professor H. B. Kirk, University of New Zealand, I owe the original suggestion

that the problem of direct development in ophiuroids should be investigated. I have also to thank Dr. Fabius Gross, of Edinburgh, for advice on the use of Erdschreiber culture medium for excised embryos, and also the Directors of Marine Laboratories at Millport and Plymouth for supplies of living and preserved material, to supplement that collected in the Firth of Forth and at Island Bay, New Zealand. The terminology employed for the germ layers is that suggested by Professor E. S. Goodrich, of Oxford, and employed by the writer in previous papers. Points of interest are discussed as they arise during the course of the paper, instead of leaving a general dicussion to the end.