An early interest in the mollusca, shown by his doctor's dissertation upon the embryology of the fresh-water mussels, printed in part in the Proceedings of the American Association, 1875, continued to be expressed in his contributions to many problems in the embryology of the fresh-water Pulmonates, of Gasteropods, of Lamellibranchs, and of the Squid. The Crustacea also rightly claimed a large share of the attention of a philosophic naturalist, bringing him face to face with the rigid formulations of law which these creatures present. The discovery of the very exceptional method of cleavage in the egg of the decapod Lucifer, and the demonstration of the existence of a free Nauplius stage there (published in the Philosophical Transactions of the Royal Society in 1882), marked a most important advance in the morphological interpretation of all Crustacea, and brought its author to the first rank as an authority upon this much-studied group. Studying and capturing at Beaufort those phantom-like sand burrowers, the Squilla, gained him an insight into and an interest in this strange division of Crustacea that enabled him to undertake that difficult task, the description of Stomatopods collected by the Challenger Expedition--a task completed in 1886. The report, published in such a magnificent series as only the British Government could have consummated, is noticeable for the author's clear, free illustration of the creatures described and classified. In it we find a classification of the numerous, weird, glassy larvæ, agreeing with the classification of the adults and marking the success of the solution of the problem--the reference of chance collections of various stages of many species to their proper places in the life history of each species.