John R. Baker

Toxicity induced in the tobacco horn-worm (Manduca sexta L.) (Sphingidae, Lepidoptera)

INSECTS feeding on toxic plants demonstrate three fairly distinct types of life-style1–3. There are cryptic species, which metabolise or rapidly excrete the toxic substances present or avoid their ingestion by selective feeding; aposematic or warningly coloured species which store plant toxins in their tissues unchanged or slightly modified4; and aposematic species which superficially resemble or mimic toxic species—without actually storing poisonous plant products—or those warningly-coloured non-storers which secrete their own toxins. It is generally agreed that the cryptic life-style is more ‘successful’ than either of the other two, which are relatively rare, and it is difficult to envisage the evolutionary steps necessary to enable a species to change to the more hazardous warning life-style. If, however, circumstances favour a switch to certain toxic host plants, a cryptic insect is frequently destined to become warningly coloured1,5. On the basis of experiments with Manduca sexta, the tobacco horn-worm, we suggest that the evolution of an aposematic poisonous insect, from the more common, harmless, cryptic type, may simply involve a change to a related food plant containing different toxic properties from those of its usual host. Storage and the acquisition of toxicity and warning colour could follow this crucial switch.

Proposed Central Publication of Scientific Papers

IN June of this year a Scientific Information Conference is being called by the Royal Society of London., to be attended by representatives of the countries of the British Commonwealth and of the United States1. A number of societies which publish scientific journals have already been invited to the Conference, and preliminary drafts of schemes to be discussed have been circulated. Among these is the draft of a provisional scheme for “Central Distribution of Scientific Publications” put forward by Prof. J. D. Bernai, the editor-in-chief of the first of the four sections of the Conference.

A. or m|[micro]| in Electron Microscopy?

IT has become customary to express measurements made by the electron microscope in A. units. I have analysed this custom by examination of Vol. 12 of Experimental Cell Research (1957). Nine of the papers are concerned with electron microscopy. A. units are mentioned twice in theoretical considerations concerned with the minimum determinable thickness of a layer of osmium, and they are also used as ordinates in graphs. These uses of the units are here disregarded, because they are not actual measurements. (The use of A. units in reports of X-ray analysis is also disregarded.) With these exceptions, I find 129 measurements recorded in A. units in reports of work in electron microscopy. The last digit of 117 of these is 0; of ten, 5; of two (both in the same paper), 7.

Practical Modern Microscopy

Traité de MicroscopieInstruments et Techniques. Par A. Policard, M. Bessis et M. Locquin. Pp. vi + 608. (Paris: Masson et Cie., 1957.) Broché, 4,500 francs; Cartonnétoile, 5,200 francs.

Scientific Literature for Enemy Prisoners of War

A SMALL organization has recently been formed1 for the purpose of sending copies of scientific papers to scientists who are enemy prisoners of war in British hands. The idea is to keep alive the spirit of discovery, so that imprisoned enemy scientists may be helped to remain mentally active and thus become useful world-citizens again after the War.

A Note on Stereoscopic Photography

IT is sometimes stated that in the stereoscopic photography of near objects it makes no difference at all to the images whether the cameras are placed parallel to one another, or convergent upon the object.

Emigration, Migration, and Nomadism

DR. F. H. A. MARSHALL has edited and prefaced this posthumous work by the distinguished authority on the sexual cycle, Walter Heape, Few books cast a wider net for readers than this. The physiologist, the natural historian, the ecologist, the anthropologist, the psychologist, even the alienist, are concerned with the subjects treated. Yet how many of these, except the physiologist, will get past the first chapter ? And how many physiologists will read the rest?Emigration, Migration, and Nomadism.By the late Walter Heape. Edited with a Preface by Dr. F. H. A. Marshall. Pp. xii + 369. (Cambridge: W. Heffer and Sons, Ltd.; London: Simpkin Marshall, Ltd., 1931.) 12s. 6d. net.

Natural History of the New Hebrides

IN a few months my brother and I are going to the New Hebrides, in the Pacific Ocean, to explore the interior of the largest island, to collect the fauna, to study animal reproduction in a climate that is almost constant throughout the year, and to undertake other work of a more special nature. Particular interest attaches to a large lake on one of the islands, said to be almost the only lake in Melanesia. We are financed in part by the Trustees of the Percy Sladen Memorial Fund.