vitamins that are essential to their host. It is common for different orders of mammals to have different gastrointestinal tract specializations, but primates are unique among mammals in having diverse digestive tract arrangements within their own order (Chivers and Hladik, 1980).

The digestive systems of primates that consume animal material are typically simpler and shorter than those of plant-eating species. The basic gastrointestinal tract of faunivores includes a simple globular stomach, a tortuous small intestine, a short conical cecum, and a simple smooth-walled colon (Chivers and Hladik, 1980).

Primate faunivores, which tend to be small and nocturnal, feed primarily on invertebrates but can supplement their diet with plant materials. The diet of the angwantibo (Arctocebus calabarenis) consists of animal prey (85%) and fruits (15%). Similarly, Galago senegalensis, Microcebus spp., and Loris tardigradus are highly insectivorous, although Galago and Microcebus supplement their diet with gums and other plant exudates. The tarsiers (Tarsius spp.) are principally insectivorous, but they also eat such small vertebrates as geckos and other lizards (Napier and Napier, 1985).

Galago has a balloon-like stomach, a relatively short small intestine, a moderate-size cecum, and a smooth, non-complex colon (Clemens, 1980). The gastrointestinal tract of Tarsius includes a colon that is about one-fifth as long as the small intestine and a spiral cecum that is half as long as the colon (Figure 1-1).

Most primates are frugivorous, but none consume diets entirely of fruit. Fruit intake is augmented with variable proportions of invertebrates, vertebrates, and other plant parts, including leaves, flowers, and exudates. The gastrointestinal tracts of primates in this broad group exhibit little structural specialization, but variations among species have been described (Chivers and Hladik, 1980).

The basic frugivorous stomach is simple and globular (Hill, 1958). The marmoset stomach has a more elongated fundus than that of cebids, which is more specialized, with a globular fundus, conical body, and cylindrical pylorus (Chivers and Hladik, 1980).

Squirrel monkeys (Saimiri), douroucoulis (Aotus), woolly monkeys (Lagothrix), and spider monkeys (Ateles) have gastrointestinal tracts comparable with those of other frugivores (Figures 1-2 through 1-4), but in most of these species, the proximal portion of the colon is expanded and haustrated along its entire length (Hill, 1960; Hill and Rewell, 1948; Stevens and Hume, 1995). The cecum itself is not haustrated (Stevens and Hume, 1995).

Marmosets (Callithrix spp.) and tamarins (Saguinus spp., Leontopithecus spp.), as well as Saimiri and Aotus, have similar diets in the wild; fruits make up the majority of foods consumed, with invertebrate prey about 20%. The larger-bodied Lagothrix and Ateles consume diets composed mainly of fruit, with various proportions of leaves and seeds. Both Cebuella and Callithrix have a “short-tusked” tooth pattern in which the lower canines are incisiform and barely longer than the adjacent incisors; such dentition enables these species to create holes in bark to extract plant exudates (sap and gums) (Izawa, 1975).

Cercopithecine primates, except colobines, have cheek pouches that permit short-term storage of harvested ingesta. The stomach of these species (Cercopithecus, Macaca, and Papio) is relatively simple and smooth-walled, followed by a short small intestine (Figures 1-5 through 1-7). The cecum is typically haustrated by three taeniae, and can support some microbial breakdown of plant material. The galago (Galago crassicaudatus) (Figure 1-8) and the ruffed lemur (Varecia variegata) are prosimians that have a prominent cecum, but the cecum of the ruffed lemur is longer and more complex than that of the galago. The cecum of the vervet monkey (Cercopithecus pygerythrus) is sacculated (Clemens, 1980).

The enlargement of the colon or cecum in gibbons (Hylobates spp.), rhesus macaques (Macaca mulatta), Syke’s monkeys (Cercopithecus mitis), and vervet monkeys (Cercopithecus aethiops) is consistent with bacterial fermentation of leaf material in the diet (Sakaguchi et al., 1991; Bruorton et al., 1991). When they are fed identical diets, the production of volatile fatty acids (VFAs, end products of microbial fermentation) in the hindgut of the more omnivorous (Morris and Goodall, 1977) baboon (Papio cynocephalus) (Clemens and Phillips, 1980) is similar to that in the hindgut of the largely herbivorous Syke’s monkey (Cercopithecus mitis) (Hill, 1966).

The rates of digesta passage among frugivorous primates depend on proportions of fruit, leaf, and animal prey in the diet. Three groups of frugivorous lemurs—Varecia variegata variegata, Varecia v. rubra, and Lemur catta— fed a similar, mixed-ingredient diet exhibited median gut passage times of 1.71, 1.69, and 4.75 hours, respectively (Cabre-Vent and Feistner, 1995). Slightly longer mean transit times (2.7 hours) were reported for Varecia v. variegata and V. v. rubra fed experimental diets containing 15% and 30% acid detergent fiber (Edwards and Ullrey, 1999a).

Fiber type, not concentration, reduced passage time from 10 to 6 hours in Callithrix jachus and Saguinus fuscicollis (Krombach et al., 1984). Fiber concentration in diets consumed by macaques had no effect on the mean transit time of either particulate or liquid markers (Sakaguchi et al., 1991).

Baboons (Papio cynocephalus) had shorter mean transit times than Syke’s monkeys (Cercopithecus mitis), when