Network and Multipolar Ganglion Cells 67 The Nerve Tissue 67 The Supporting Lamella 68 Epithelium of Ampulla and Floating Cells 68 The Endothelium of the Peduncle 73 The Tentacles and Pedalia-- The Ectoderm 74 (a) Thread Cells 74 (b) Muscle Fibers 74 (c) Ganglion Cell 75 The Endoderm 75 SUMMARY 77 LITERATURE 78 REFERENCE LETTERS 80 DESCRIPTION OF FIGURES 81 INTRODUCTION. This paper may be regarded as a continuation of the Cubomedusan studies pursued by Dr. F. S. Conant while in Jamaica, in 1896 and 1897, with the Johns Hopkins Marine Laboratory. His systematic and anatomical results have since been published as his Dissertation (“The Cubomedusæ”) by this University. Conant described this paper as Part I, hoping soon to add a second part on the physiology and the embryology, for which he had some notes and material at hand. Returning, however, to Jamaica with the laboratory, in 1897, he continued his physiological experiments, and preserved material for histological purposes. Upon the untimely death of Conant, his material and notes were placed in my hands by Professor Brooks, to whom I here take the opportunity of expressing my appreciation and sincere thanks for the honor thus conferred and for the many favors received. In this paper I shall note at some length Conant’s physiological results and append his notes. I shall also add my results on the histology of the eyes and the sensory clubs in general, with some few facts on the histology of the tentacles. The embryology will be reserved for a future paper. The forms used in the physiological experiments were Charybdea Xaymacana, one of the two species (see Literature V, a and b) first found and described by Conant; Aurelia aurita; Polyclonia and Cassiopœa. The greater number of Conant’s notes are on Charybdea, and were left by him just as taken at the time of experimenting. Many of these notes are highly interesting and in the main fit in well with Romanes’[I] and Eimer’s[IV] results.