In a recent paper (Mackenzie and Muller, 1940) a brief account was given of certain methods employed to obtain a favourable mutation rate in male adult Drosophila. These methods were largely empirical, and a detailed account of their development, together with a discussion of their significance, seemed rather beyond the scope of the paper, which dealt principally with the possible chromosome rearrangements which could be brought about by ultra-violet light. Hence only the average of a large number of experiments was given. In this paper it is proposed to give a fuller account of the influence of ultra-violet rays on Drosophila, and to compare the somatic effects, which are directly lethal, with the spermatic effects, which occur in the surviving insects and are observed as mutations in the offspring.

The apparatus described was developed in connection with a study of the growth and development of the stick insect, Dixippus morosus. The principle is that of simple displacement, and consistent results are obtained with objects as small as 0·007 millilitre.

In recent years considerable progress has been made in the investigation of the biochemistry and physiology of the root nodules of leguminous plants (Wilson, 1940). It now appears desirable that the anatomical structure of the nodule should be re-examined from the standpoint of the functions which the nodule is considered to discharge. Special interest attaches to the distribution within the nodule of endodermis, cork, and any other suberized layers, since on this will depend the facility with which materials may be exchanged between the tissues of the nodule and the environment. There is some confusion in the literature as to the distribution of such suberized tissues within the nodule, but it is clear that rather curious features are presented.

A cytological study of the testes of the cat was undertaken in order to disclose the structural differentiation of the sex chromosomes. It was hoped that an analysis of these particular chromosomes in the male sex during meiotic division might reveal structural peculiarities which would throw some light upon the highly complex genetical behaviour of tortoise-shell cats.

Treatment of the immature animal with æstrogenic or gonadotropic substances has been described by a number of authors in diverse experiments, and vaginal cornification, enlargement and typical histological changes in the uterus, ovulation, mating, and fertilisation, have all been produced, but no successful implantation. The histological changes which occur in the uterus and vagina of the treated immature animal are considered (Reynolds and others) to be characteristic of heat and similar to those in the adult uterus during heat. Nevertheless, it is suggested that the failure to procure implantation in treated immature animals may be due to an unfavourable condition of the uterine endometrium. If that is so, there must exist some difference between the response of the treated immature uterus and that of the mature uterus during cestrus which has thus far escaped detection. Recently we have described (Bacsich and Wyburn, 1940b) a cyclic vascular change in the uterus of the guinea-pig in the form of antimesometric hyperæmia present only during normal heat, and, moreover, have been able to induce this vascular response in spayed animals by hormonal treatment (Bacsich and Wyburn, 1941). As this cyclic vascular change provides a particularly delicate test of a complete response of the uterus to ovarian hormonal activity and may influence the site and the course of implantation, it seemed of interest to ascertain if the “characteristic” œstrogenic response of the immature uterus included antimesometric hyperæmia.

It is well known that the dimensions of the ammonite shell conform approximately with the properties of a logarithmic or equiangular spiral. An illuminating account of the logarithmic spiral in its application to the growth of molluscan shells is that given by Sir D'Arcy Thompson (1917, pp. 491–586, and 1942, pp. 748–849). His formula relating the spiral angle of the shell and the ratios of certain linear dimensions must be useful to all interested in shell form in molluscs.

The problem of viability and fertility of interspecific hybrids in Drosophila has been attacked most recently by Muller and Pontecorvo (1941). They crossed diploid Drosophila simulans males with triploid melanogaster females, and, by using a specially designed technique, succeeded in introducing into the marked genotype of melanogaster some chromosomes of simulans. Amongst the many interesting results obtained, it was found that not all interspecific combinations of chromosomes were viable; the large chromosomes of one species show a definite “need” for some genes or group of genes in other chromosomes of the same species, and these authors have drawn the conclusion that there are a number of complementary “lethals” in both species located in the major chromosomes (X, II, and III).

In previous contributions the writer has described the structure and behaviour of the mitochondria and Golgi material of the egg of the mouse (Gresson, 1933, 1938 and 1940 b), and more recently has traced the cytoplasmic inclusions through the stages of maturation, fertilisation and the first cleavage division (Gresson, 1941). As the result of observations on the sperm middle-piece it is claimed that the mitochondria of the sheath are liberated into the ooplasm of the fertilised egg, and are shared out between the first two blastomeres; and further, that a Golgi element is present in the middle-piece, and that this breaks up and its products are distributed through the cytoplasm of the fertilised ovum (Gresson, 1940a, and 1941).

In 1930 ovulation in ferrets outside the breeding season was obtained by Hill and Parkes (1930) by means of gonadotrophic extracts. Later, similar results were obtained in sheep and thus it became possible to induce pregnancy outside the normal breeding season (Cole and Miller, 1933), and its practical importance was investigated by Parkes and Hammond (1940). Similar experiments on the golden hamster, Cricetus auratus, are described below, as this animal has proved to be a most interesting subject for the study of sex hormones (Klein, 1937 and 1938; Peczenik, 1942).

A cytological analysis of a number of Sealyham, Spaniel, and Spaniel × Manchester Terrier dogs was undertaken in order to determine the number and structure of chromosomes during both mitosis and meiosis in each breed, and to ascertain the differences between them in respect of chromosome number and behaviour.

Various species of the lamellibranch Gryphœa have received much attention from palæontologists in the past twenty years, partly because careful collecting appears to have produced continuous series of forms (lineages) and partly owing to the problems which are raised by their progressive development from more normal oysters.