Two series of logarithmic expansion systems are described, with × 1·6 as the rate of increase in numbers of new monotypic genera correlated with a rate of × 2·0 for increase in total numbers of species. These series are discussed in relation to current numbers for monotypic genera, total genera, and total species in 36 of the largest 45 families of flowering plants.

Marking experiments have demonstrated that certain of the rings appearing as surface sculpture on the shells of the lamellibranch Venerupis pullastra are valid as a measure of annual growth. From measurement of these rings the mean monthly and the mean annual growth increments have been calculated. The length-age relationship curve is similar to that of most other lamellibranchs. Reasons for the variation in the mean monthly rate of growth have been examined. The height-length and the thickness-length ratios for various sizes have been calculated and found to follow a simple and direct tangent relationship.

From the proportion of first births in any year it is possible to calculate the average size of fertile family which would be produced if the rate of reproduction remained constant and equal to that of that year. From marriage age and total married fertility rate the corresponding size of all families may be estimated. The relation of these two figures gives the percentage of fertile unions corresponding to the aforesaid reproduction rate. The proportion of fertile unions in various countries during the two wars, and under the varying economic conditions of peace, has been studied, and the great variations demonstrated. The importance of these variations is considered.

This paper is a first report on the Echiurids and Sipunculids of Zanzibar, and deals with the material collected by Dr J. D. Robertson during the years 1948–1950 on the shores of Zanzibar, supplemented with a few dredgings. These collections contained two species of Echiurids and eighteen species and varieties of Sipunculids. Of these, one Echiurid (Ochetostoma zanzibarense) and two Sipunculids (Dendrostoma robertsoni and Phascolion robertsoni) are described as new species. Six others are recorded from the area for the first time. The list of species now described from the Zanzibar area contains eight species of Echiurids and twenty-four species and varieties of Sipunculids. Rich as the area is in species, it is even more remarkable for the numbers of individuals, some species being dominant forms in the population.

In each of three years studied, the spring hatching period for a flock of Brown Leghorns has been divided into two sub-periods such that a number of matings are represented by offspring in each sub-period. Analysis of variance of age at sexual maturity reveals statistical interaction between family means and hatching period, the ranking of family means varying with date of hatch. Consequences of this are discussed with reference to current methods of correcting age at maturity for date of hatch, the method of multiple shift progeny testing, and the general question of improvement by selection in the presence of non-additive combinations of genetic and environmental effects.

Measurements of comb growth in maturing pullets reveal a seasonal retardation, possibly reflecting retardation in sexual maturity, and in line with environmental effects causing cessation of production in older birds. It is suggested that rapid changes in day length during September and October may play a large part in determining the retardtions and interactions displayed, and that measurements of comb growth may be of value in recognising consistently superior genotypes for age at sexual maturity.

A method is presented by which the sampling variance of all heritability estimates derived from ratios involving variance components may be found.

The birthcoats of both coarse and fine-fleeced sheep can be separated into different types of fibres. Each type of fibre is formed by a particular type of follicle. The ratios of the different types of follicles are the same in all the breeds of British sheep studied, and therefore variation of the follicle population can be excluded as a factor in the evolution of the British types of fleeces. Some birthcoats are coarse, others are fine, and some birthcoats are short, others long. The two differences are independent both developmentally and genetically. In the few lambs studied, the coarse type is dominant over the fine type, and the short type is dominant over the long type. It is suggested that the Down shortwool fleece evolved along a different route from that which gave rise to the Merino shortwool fleece.