When, in 1865,1 communicated to the Royal Society the First Part of Monograph on the Anatomy, Physiology, and Development (excluding he earliest stages previously described by Prof. Wyville Thomson) of animal which might be regarded—except in certain comparatively unimportant particulars—as a type-form of the whole Crinoidal series, I had nearly concluded my investigation of the subject of it, that I fully ontemplated the presentation of the Second and concluding part in the course of a year (Jr two. Uncertain health, however, interfered with its ompletion in the first instance; and my spare time has since then been;o far taken up by the various inquiries that have arisen out of the Deep-Sea researches which I prosecuted in the vacations of 1868 and three following years, that I have found myself quite unable to resume the tudy of
Antedon
. Thus it comes to pass that, though I have now had me for a period of ten years the results of my previous labours, as presented in several hundred preparations, with a series of most admirable Ira wings executed by Messrs. George West and A. Hollick, illustrating almost every point of primary importance not only in its structure, but also in the history of its development from nearly the earliest Pentacrinoid stage, all this material has remained unpublished; for I have felt that the completion of my Monograph in a manner worthy of its subject required that certain obscurities should be dissipated and certain gaps filled up; and it now, also, becomes desirable that the Histology of this type should be more fully elucidated by the aid of modern appliances, and that the earliest phases of its Development should be thoroughly reinvestigated. I especially desire to ascertain whether the free-swimming larva (or pseudembryo) has a
Gastrcea
stage, and to follow out the derivation of the gastric and perivisceral cavities of the Pentacrinoid, and of its original tentacular system, from the structures of the pseudembryo—points on which Prof. Wyville Thomson’s Memoir, admirable as it is, does not enlighten us. This stage of the history has been subsequently studied by a most able observer, Herr Metschnikoff; and the conclusions he has arrived at in regard to the origin of the tentacular system I find to be essentially accordant with those which I had drawn from my own researches on a later stage.
Ultrastructure of the ciliated cells of the free-swimming larva, and sessile stages, of the marine spongeHaliclona indistincta(Demospongiae: haplosclerida)