There can be little doubt that, to use the parlance of the advertising world, the elasmobranch fishes have a "high profile image" in today's world. To most mem­ bers of the general public they are seen as terrors of the deep, perfect aquatic predators, and the stars (or more acurately, the villains) of major Hollywood movie films and innumerable television nature programmes. Such an image belies the fact that the vast majority of elasmobranch species feed on invertebrates and that, for man, the threat from shark attack is infinitesimal compared with even being struck by lightning! Similarly, there can be few biologists who have not carried out the classic vertebrate dissection of the dogfish at some stage early in the formative years of their scientific education. Yet elasmobranch species make up only a small proportion, perhaps little more than I %, of all vertebrates, and there are probably nearly 50 times as many teleost species as there are elasmobranchs. It is also curious that, as subjects for modern research, elasmobranchs seem to be chosen sometimes for their unique physiological characteristics and at other times because they represent excellent model systems for the study of some general process. Equally, it is for both these, seemingly contradictory, reasons that this book was proposed.