Examination of living embryos has shown that the heart is a functionally active organ from a very early stage of its development. At all periods of life the result of the functional activity is in essentials the same, viz. the propulsion of the blood in a definite direction through the heart into the vessels arising from it; but the mechanism for effecting this propulsion undergoes profound alterations, and the heart becomes transformed from a simple continuous tube, destitute of valves, whose walls contract in a rhythmic peristaltic wave, into a complex four-chambered organ, divided into right and left portions, which are ultimately completely separated from one another, possessing valves, and contracting not in a peristaltic wave but in alternating consecutive contractions of the atria and ventricles of the right and left sides simultaneously. Coincidently with the changes in the heart itself, profound alterations occur in the vessels leading to and from the heart. In this combination of simultaneous development and functional activity the heart differs from the other organs of the body, and hence its development presents special problems involving the function as well as the structure of the different parts. Our knowledge of the development of the heart in man cannot yet be said to be complete.

A few words of explanation are necessary at the outset in connection with the terms used in association with the animals upon which these investigations were made.

Dealers in ferrets supply two types of animals—one with yellowish-white fur and pink eyes, which they call “ferrets,” and a second type in which the yellowish fur is intermingled with a varying admixture of brownish or brown-black hairs; the second type they call “polecats.” The polecats of the ferret-dealers are not, however, true polecats, for Miss Frances Pitt, who has bred ferrets and polecats and ferret-polecat hybrids in a scientific manner, and to whom I am indebted for the greater and best part of my information on this subject, points out that the so-called polecat of the dealers is never so dark and handsome in colour as the true polecat. Moreover, as Miss Pitt states, in the true polecat the light marks in front of the ears do not usually join across the forehead, whereas in the polecat of the dealers they form a band across the face; further, when viewed from in front and above, the head of the true polecat has the form of a fairly equilateral triangle, whilst in ferrets and the so-called polecats of the dealers the head, on the whole, has the form of an isosceles triangle.

A number of rare genera of Ferns of somewhat uncertain affinity had recently come to my hands. As they had by previous writers been referred in some degree to a common relationship it seemed well to embody them together in one memoir. As the work proceeded thejustification of this became more apparent, and towards the end of the work the conclusion seemed clear that the suggested affinities were real though not very close.

Several attempts have already been made to interpret the well-established results of biometry in accordance with the Mendelian scheme of inheritance. It is here attempted to ascertain the biometrical properties of a population of a more general type than has hitherto been examined, inheritance in which follows this scheme. It is hoped that in this way it will be possible to make a more exact analysis of the causes of human variability. The great body of available statistics show us that the deviations of a human measurement from its mean follow very closely the Normal Law of Errors, and, therefore, that the variability may be uniformly measured by the standard deviation corresponding to the square root of the mean square error. When there are two independent causes of variability capable of producing in an otherwise uniform population distributions with standard deviations σ1 and σ2, it is found that the distribution, when both causes act together, has a standard deviation . It is therefore desirable in analysing the causes of variability to deal with the square of the standard deviation as the measure of variability. We shall term this quantity the Variance of the normal population to which it refers, and we may now ascribe to the constituent causes fractions or percentages of the total variance which they together produce. It is desirable on the one hand that the elementary ideas at the basis of the calculus of correlations should be clearly understood, and easily expressed in ordinary language, and on the other that loose phrases about the “percentage of causation,” which obscure the essential distinction between the individual and the population, should be carefully avoided.

The prostates or spermiducal glands form a prominent feature in the anatomy of the large family of the Megascolecidæ. Occurring in the neighbourhood of the termination of the sperm-ducts, they assume one of two forms, the tubular or the lobular. In the first, the gland typically takes the form of a bent, undulating, or coiled tube, cylindrical, with a single central lumen; in the second, it consists of a loosely or tightly packed aggregate of lobules, each with its ductule. The prostatic duct is in the first case a continuation of the glandular tube; in the second, the duct is formed by the union of the ductules; in both cases it is as a rule firm and muscular.

The calciferous glands of earthworms are well-known structures, which occur under a variety of forms, and have been the subject of a considerable amount of research. They are appendages of the oesophagus which occur in different segments in different genera and species; and the usual view of their morphological nature, put forward by Beddard (l) in 1895, and for long generally adopted, is that their epithelium is the oesophageal epithelium thrown into various degrees of folding. Beddard describes these different degrees in a number of different forms.

This investigation on the morphology of the Fore-brain or Prosencephalon of Elasmobranchii was suggested to me by Professor G. Elliot Smith, F.R.S., and I am indebted to him for introducing me to an interesting if somewhat difficult and perplexing subject. A glance at the literature on the morphology of the prosencephalon will readily convince one of two things—firstly, of the endless field for work in endeavouring to ascertain the true homologies of the neurone areas and fibre tracts in the brain throughout the Phylum Vertebrata; and secondly, of the somewhat unnecessary obstacles which have been introduced into the problem by the more recent additions to a terminology, already overburdened and encumbered, of new terms for equivalent parts. It would appear to be very advantageous if mutual agreement could be arrived at among workers on this subject regarding the use of descriptive terms, and, if such is at present impracticable, that each new worker should refrain as far as possible from applying a new term to a structure already previously described. In one case, namely, that of the tuberculum olfactorium, five different terms have apparently been applied to the same area.