An amiable brief for zoos--today's commodious, carefully-run zoos--as the only hope of preserving endangered animal species. Bendiner first covers some very familiar ground: the practical uses of animals for research (the tsetse fly and genetics, the rhesus monkey and the Rh factor) and as part of the web of life; the soaring rate of extinction, the disappearance of some species (yes, the last passenger pigeon, the great auk, the dodo), the number and variety now endangered; the specific threats--from commercial hunting, territorial encroachments, tourism in game preserves. Against that background--rudimentary to anyone with the least interest in the subject--Bendiner comes to the heart of the matter: zoos not as showcases but as breeding grounds committed, moreover, ""to reducing the number of species"" each holds ""and increasing the number of specimens."" For successful breeding, he learned, attention must be paid to the species' natural mating habits (cheetah pairs, confined, grow apart; herd animals tolerate only a single adult male) and to providing suitable (not necessarily spacious) quarters--with ""at least some of the functional points and facilities around which the inmates' life revolves"" (like the synthetic termites' nests devised, for zebras to rub against, by Zurich's Dr. Hediger). The touchy problems of eliminating surplus animals (those redundant herd males, the burgeoning lion population) and of ""training acts"" come up too--the latter in the context of relieving boredom. Are such shows ""demeaning to the performers and in any event unnatural?"" Or, as Bendiner seems inclined to think, do they keep animals sufficiently ""alert and active"" to flourish in captivity, and procreate? He also takes note of those who grant the zoos' success in saving endangered species but still object that 1) zoo animals are not wild animals and 2) the possibility of returning them to the wild is slight. To the last he has to assent--the evidence, though scanty, is not encouraging. But: ""to have preserved some wild animals""--albeit slightly altered--""is vastly better than having no animals, either in zoos or in the wild."" With some concluding remarks on standards and funding, and the official list of threatened species, a popular introduction that at least touches on all the pertinent aspects of a critical, contested situation.