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A really good preservative solution-one not only protecting from mould and decay, but also preserving the natural transparency and colours of the tissues, while giving them a serviceable firmness-is yet to be discovered. Alcohol, in other respects perfect, has the great disadvantage of destroying both colour and transparency, and glycerine, though almost free from these defects, is a most unpleasant medium, on account of its density and stickiness. On the whole, a saturated solution of boracic acid in glycerine, diluted with three or four parts of water, has given in my hands the best results ; but my preparations so made have not yet had sufficient time for fair trial. 2 This statement refers to the preserved specimens sent to Dr. Brady. As a matter of fact, Copepoda were rarely, if ever, absent from the tow-net gatherings when examined on board ship.-J. M.

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In preparing this monograph it was not part of my plan to enter at all into the consideration of the physiology or internal anatomy of the Oopepoda, but, in compliance with the wishes of some of my friends, expressed while the first volume was passing through the press, I have put together, in the form of a preface to this third volume, a condensed account of some of the more important observations which have hitherto been made on this part of the subject. It will be at once apparent that what I have attempted is nothing more than a general outline, in the production of which I have been greatly indebted to the works of Glaus, Gegenbaur, and Huxley. Had I included the truly parasitic species, in whose anatomy, physiology, and general habits of life so many points of the highest interest occur, I should have been travelling beyond VOL. III. A 2 BRITISH COPEPODA. the professed limits of my work, and have extended this preface beyond reasonable bounds,-on which account those species are noticed in the most cursory manner, and only in elucidation of the proper subject of the memoir. The non-parasitic Copepoda may be described as Entomostraca, having an elongated body of variable form, but generally cylindrical, without a bivalved shell, and showing more or less completely a division of the body into numerous rings, or somites. There are two pairs of antennse, three pairs of prehensile and masticatory, or suctional, mouth organs, and five pairs of feet, adapted chiefly for swimming. The females are mostly fertilized by means of spermatophores ; the ova are usually carried in external ovisacs ; when first hatched the larvse have only three pairs of limbs, and go through several metamorphoses before attaining the mature form. The parasitic species, at one end of the series approach very nearly in structure and general appearance to the non-parasitic ; at the other end they are extremely different, exhibiting, especially in the males, many most remarkable examples of retrograde development, so that without the study of their metamorphoses it would be quite impossible to recognise them as Copepoda, or even as Crustacea of any kind. Yet even in these degraded forms-at any rate in the females--natatory limbs in a very much atrophied condition are almost constantly found. General eorm. -The animal is usually somewhat pear-shaped, rounded in front and tapering towards the GENEEAL ANATOMY. 3 hinder extremity, convex on the dorsal and flattened on the ventral surface. The degree of dorsal convexity, however, is variable, the most common form of the body being sub-cylindrical, but in many cases-notably amongst the Poecilostoma, Siphonostoma, and in some genera of the Harpacticidge (Zaus, Peltidium, Por-ceUidmm, Idya, ScuteUidium) -the animal is markedly flattened, constituting a type of structure almost as widely distinct from the normal Copepoda as are the Isopoda from the Amphipoda, amongst the sessile-eyed Crustacea.But in the genera of Harpacticidge here referred to, the flattened form does not coincide with any deep-seated ...

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