In recent years, because of advances in karyological techniques, we have witnessed a remarkable renewal of interest in studies of mammalian chromosomes. These techniques, generally involving the use of tissue culture, colchicine and hypotonic solution pretreatments, allow for a much clearer display of metaphase chromosomes of mammalian cells than the classic direct squash or tissue section methods. Consequently, what was known about the chromosome complement of most mammals must be revised. The most astonishing revision, of course, was that made by Tjio and Levan in 1956, who demonstrated that the diploid number of man is 46, not 48 as previously believed. Similar revisions will have to be made for many other mammalian species, either in number or in karyotype structure. Many animals are being examined cytologically for the first time. The findings are now extensive and scattered; they appear in numer­ ous periodicals and newsletters, or they are kept in cytologists' file drawers without being published. It is difficult to have access to perti­ nent data for comparison among related species or for evaluation of various karyological characteristics within a karyotype. Such evaluations can be done only when reasonably uniform material is collected and placed side by side for comparison, accompanied by relative references. We considered that probably an Atlas of Mammalian Chromosomes would fulfill such a need. Needless to say, it is impossible to present karyotypes of all mam­ malian species at one time.

Marsupialia.- Macropodidae.- 1 Potorous tridactylus apicalis (Rat kangaroo).- Chiroptera.- Desmodontidae.- 2 Desmodus rotundus murinus (Vampire bat).- Vespertilionidae.- 3 Pipistrellus subflavus subflavus (Cave bat).- 4 Pipistrellus subflavus subflavus (Eastern pipistrelle).- Edentata.- Dasypodidae.- 5 Dasypus novemcinctus (Nine-banded armadillo).- Lagomorpha.- Leporidae.- 6 Lepus alleni alleni (Antelope jack rabbit).- 7 Lepus californiens eremicus (Black-tailed jack rabbit).- 8 Oryctolagus cuniculus (Laboratory rabbit).- Rodentia.- Sciuridae.- 9 Marmota monax (Northeastern American woodchuck).- 10 Tamiasciurus hudsonicus streatori (Red squirrel).- Heteromyidae.- 11 Perognathus intermedius (Rock pocket mouse).- Cricetidae.- 12 Baiomys taylori subater (Northern pygmy mouse).- 13 Cricetulus griseus (Chinese hamster).- 14 Mesocricetus auratus (Syrian or "golden" hamster).- 15 Microtus pennsylvanicus pennsylvanicus (Meadow vole).- 16 Onychomys leucogaster (Northern grasshopper mouse).- Muridae.- 17 Mus musculus (Mouse).- 18 Rattus norvegicus (Rat).- Chinchillidae.- 19 Chinchilla laniger (Chinchilla).- Carnivora.- Canidae.- 20 Canis familiaris (Dog).- 21 Canis latrans (Coyote).- Ursidae.- 22 Selenarctos thibetanus (Asiatic black bear).- 23 Ursus americanus (American black bear).- Procyonidae.- 24 Bassariscus astutus (Ringtailed cat).- 25 Procyon lotor (North American raccoon).- Mustelidae.- 26 Mephitis mephitis (Striped skunk).- 27 Mustela putorius furo (Ferret).- 28 Spilogale putorius (Spotted skunk).- Viverridae.- 29 Actictis binturong (Binturong).- 30 Suricata suricatta (Mierkat).- Felidae.- 31 Felis catus (Domestic cat).- 32 Felis pardalis (Ocelot).- Perissodactyla.- Equidae.- 33 Equus asinus (Donkey).- 34 Equus caballus (Domestic horse).- 35 Equus hemionus onager (Persian wild ass, Onager).- 36 Equus przewalskii (Mongolian wild horse).- 37 Equus zebra hartmannae (Mrs. Hartmann's mountain zebra).- Artiodactyla.- Suidae.- 38 Sus scrofa (Domestic pig).- 39 Sus scrofa (European wild boar).- Camelidae.- 40 Vicugna vicugna (Vicuna).- Cervidae.- 41 Dama dama (Fallow deer).- 42 Odocoileus hemionus (Mule deer).- 43 Odocoileus virginianus (Whitetailed deer).- Bovidae.- 44 Bos taurus (Cattle).- 45 Ovis aries (Domestic sheep).- Primates Callithricidae.- Callithricidae.- 46 Callithrix jacchus (Common marmoset).- 47 Cebuella pygmaea (Pygmy marmoset).- Cercopithecidae.- 48 Cercopithecus aethiops sabaceus (Vervet monkey, African green monkey).- Pongidae.- 49 Pan troglodytes (Chimpanzee).- Hominidae.- 50 Homo sapiens (Man).