From all the facts which the study of the Hydroida has made apparent, we may regard it as certain that however long zooidal multiplication may continue, this is not sufficient for the perpetuation of the species, but that a period must at last come in the life of the hydroid when by an act of true sexual reproduction, new individuals are produced for the indefinite extension of the species through time.

Independently of the general agreement which necessitates the association of the Hydra, Actinia, and other Cœlenterate animals into one primary group of the animal kingdom, we must also expect a special morphological correspondence between the various forms of animals thus associated. In other words, a homological agreement ought to be determinable between the parts of animals included in any one subordinate section of the Cœlenterata with the parts of animals included in any other.

A comparison of the two primary sections of the Cœlenterata (Actinozoa and Hydrozoa), and of the various orders of these with one another, will show that such an agreement really exists, and that it is possible, by easily understood and thoroughly consistent modifications, to convert each special type into any of the others.

The distinguished French naturalist, Professor H. Milne Edwards, in the ninth volume of his valuable Lectures on Comparative Anatomy and Physiology, published only last year, when referring to the fœtal membranes in the Cetacea, states, that much information is still required to complete our knowledge of that subject.

It may perhaps be advisable, before I commence to describe the results arrived at by my recent dissections, to give a brief account of the observations made by previous inquirers into this department of anatomy, so that we may more clearly recognise wherein our deficiencies lie, and the direction in which our researches ought to be conducted, in order to render our information as complete as possible.

The innervation of the vascular system is a subject which has engrossed the attention of physiologists ever since the days of Galen. Yet, notwithstanding the number of distinguished observers who have contributed to our knowledge of this difficult topic, there are still many points of the greatest importance which are enveloped in the deepest obscurity, and not a few regarding which opinions are much at variance.

No subject of modern scientific inquiry is more important than the series of deposits in which geology comes in contact with the period of human history. This must be my apology for some of the seemingly trivial details contained in the following paper. When these observations were begun, nothing could be further from my thoughts than any reference to the antiquity of man. But I shall perhaps best introduce the subject by simply narrating the way in which I was led forward step by step, till the whole inquiry assumed the form in which it is here presented.

It is well known that although the overwhelming majority of specimens of fircones exhibit one or other of the simple spiral arrangements represented by the terms of the ordinary series ½, ⅓, ⅖, ⅜, , &c., whose generating and successive secondary spirals are indicated by the numbers 1, 2, 3, 5, 8, 13, &c., yet exceptional cases occur now and again, where we find either conjugate spirals of the ordinary system, or arrangements (usually simple, but sometimes conjugate) belonging to other systems of spirals. Of these exceptional arrangements, perhaps the most common are bijugates of the ordinary system, giving the numbers 2, 4, 6, 10, 16, 26, &c., and simple spirals belonging to the system ⅓, , &c., giving the numbers 1, 3, 4,7,11, 18, &c. More rarely, trijugates of the ordinary system occur, giving the numbers 3, 6, 9, 15, 24, 39, &c.; or spirals of the system , ⅕, , &c., giving the numbers 1, 4, 5, 9, 14, 23, 37, &c.; not to speak of various other arrangements, some of which will fall to be considered in the special cases which form the subject of the present communication.

It is familiarly known as one of the commonest experiments in optics that when a beam of polarised light is passed through a thin film of mica or selenite, and subsequently analysed either by reflection or by double refraction, two colours are seen complementary to one another, and alternating with one another at each 90° of a revolution of the analysing plate or prism.

The combined researches of Anderson and Williams on the basic compounds contained in coal tar have led to the discovery of two well-defined series of organic bases, called respectively the Pyridine and Chinoline series, the members of both of which possess the properties of nitrile bases. The isomerism between the pyridine and the aniline series of bases excited considerable interest at the time of its discovery. The subsequent researches of Williams on the products of the distillation of chinchonine led to the discovery of bases having the same composition as the members of the pyridine and chinoline series of coal tar. When first discovered they were supposed to be identical. Since that time, however, a careful examination and comparison of the tar series of bases with the chinchonine series has led Mr Williams to the interesting discovery that the two lutidines, as also the two chinolines, are in reality not identical, but isomeric. This introduces a greater complexity into the study of the constitution of these compounds.