In his work on the “Present Evolutionary Tendencies and the Origin of Life Cycles in the Uredinales”, Jackson (1913, p. 7) has pointed out that the general impression among mycologists, until quite recently, has been that the life cycles in existing species of rust are quite definitely fixed. In a review of the small amount of literature that has appeared on this subject, he has shown that this conception is not altogether true, and that it is not at all difficult to find species of rusts which exhibit evidence of being in an unstable condition with reference to life-history. As the literature which he has quoted is almost exclusively American and deals with American species only, it might be inferred that this instability of life-history is not found elsewhere. The purpose of this paper is to review the European literature on this subject, and to describe the occurrence in Great Britain of four rust species of which the life-history is in an unstable condition.

Previous reports (Black, 1943, 1945) on the resistance of potatoes to the blight fungus (Phytophthora infestans) have shown the existence of at least two major genetic factors (Ra and Rb) in the host, and the occurrence of not less than two strains (A and B) of the pathogen.

From the studies then reported, it was concluded that the two genes had been brought into the potato from different phyletic sources and that one, Ra, when in the dominant state, conferred resistance to strain A, while similarly Rb conferred resistance to strain B.

There are two commonly met with types of defective eggs laid by the domestic hen that result in considerable financial loss to the poultry farmer, and are frequent enough in their occurrence to affect perceptibly the potential food supply derived from the poultry industry.

The first of these results from the inclusion of blood or meat spots in eggs, and the second is the production of eggs so small as to make the majority of them unsaleable—the so-called “Miniature” eggs.

The presence of blood on the yolk of an egg was recorded by Aristotle as early as 300 B.C., and he attributed it to premature ovulation. Later, about A.D. 1600, Fabricius (Adelmann, 1942), during a demonstration of “sanguineous” eggs to his anatomy class, described a livercoloured body included in an egg. The occurrence of blood spots in eggs led both these authors to propound the theory that the yolk was directly formed from blood.

The rapid spread of bracken in some parts of the country has led to considerable investigation into the habits of the plant. But in almost all cases it is the spread of the adult sporophyte which has been described, and little attention has been paid to the insignificant, complementary half of the life cycle—the prothallus. Nor does any attempt appear to have been made to assess the rate of development of the prothallus and the young sporeling. A recent attempt to collect records of the occurrence of prothalli and young sporophytes in the field has shown how seldom they are found, and has emphasised the fact that little is known of the extent to which the plant spreads by the initiation of new colonies from spores (White, 1930).

The present paper gives an account of the behaviour of the Golgi material, mitochondria, and nucleolar extrusions during the oogenesis of dog, cat, and rabbit. So far as the writer is aware there is no previous detailed work on the cytoplasmic components of the female germ-cells of the animals investigated.

R. Vander Stricht (1911) dealt with the oogenesis of the cat; O. Vander Stricht (1923) has made a comparative study of oogenesis of mammals, including the dog and the cat; P. del Rio Hortega (1913) described the behaviour of the Golgi material, and H. von Winiwarter (1900) studied the nuclear changes during oogenesis of the rabbit; H. von Winiwarter and G. Sainmont (1909) dealt with nuclear metamorphosis during the oogenesis of the cat; finally J. Nihoul (1926), in his paper on the rabbit, described the Golgi material during oogenesis. All the papers quoted, apart from those which deal with the nuclear changes, are either incomplete surveys, or the methods used are insufficiently delicate to reveal changes shown by modern techniques.

The South African clawed toad, Xenopus Iœvis, ovulates and extrudes its eggs into the water after injection of gonadotropic extracts (Hogben, 1930). Xenopus has been shown to be a most satisfactory test animal for the detection of chorionic gonadotropin in the urine of pregnant women, provided the toad is in good condition. In the last ten years much work has been done on the husbandry and breeding of these animals and good laboratory conditions specified (Alexander and Bellerby, 1938; Landgrebe, 1939; Landgrebe and Purser, 1941; Gasche, 1943; Landgrebe and Samson, 1944). This toad has many advantages over other test animals. It lives indefinitely in the laboratory; the author has kept some animals for over twelve years, and they still respond to injection of gonadotropic extracts by ovulation and extrusion of eggs into the water. Recognition of this response does not necessitate killing the animal. Since Xenopus never ovulates spontaneously under normal laboratory conditions and does not extrude all its eggs simultaneously after an injection of gonadotropic extract, it can be used repeatedly. Each toad can be used at least twenty-four times under the conditions specified. The animals can be kept in good condition without much demand on laboratory routine. They need feeding and cleaning only once a week. The toads are very viable. Apart from the few deaths which often occur soon after a new stock arrives in this country, the writer has lost only eight animals in the last three years, during which time the average number kept was 500 and the number of test injections exceeded 5000. If kept at 22° C. the normal animal in good condition ovulates and extrudes eggs into the water within 24 hours after the single large dose of gonadotropic substance used in routine pregnancy diagnosis. These advantages, and the possibility of realising a simple 24-hour quantitative assay of chorionic gonadotropin, prompted an investigation into the use of the toad as a test animal for this purpose. Necessary preliminaries include inquiry into the effect on sensitivity of (1) temperature, (2) light, (3) weight of animal, (4) repeated use, and (5) route of injection. These points have been investigated with a view to the discovery of the most important variables. All the animals used have been in captivity for many years, and had previously been used many times for routine Hogben tests for pregnancy.