The prey is, of course, swallowed entire, and the recently swallowed items squeezed from the stomachs provide the best material for the study of food habits. However, relatively few racers had detectable food items in their stomachs; digestion is rapid and often the snake was in a trap for a day or more before it was found. Therefore the greater number of records were obtained from scats. The residue in scats consisted entirely of hard and indigestible parts such as the chitin of insects' exoskeletons and the hair, feathers, scales, teeth and occasional bone fragments of the vertebrate prey. The insects eaten could usually be counted individually by sorting parts, such as heads or hind legs. With mammals, birds and reptiles the hair, feathers, or scales did not permit counting of individuals--each occurrence was assumed to represent one individual but in some instances two or more may have been present. Amphibians, lacking indigestible dermal structures were in most instances not represented at all in the scats, since their tissues were more or less completely dissolved by the digestion of the snakes. Soft-bodied larvae of insects and other invertebrates conceivably could be likewise completely digested, but such occurrences must be rare, as most of the invertebrates known to be eaten have the mouth parts, at least, heavily chitinized. Admittedly the factors discussed above would cause some bias in the percentage composition of the food determined from scats, but I believe that the amount of error introduced was slight, because, judging from the records of items from stomachs, amphibians are not eaten frequently, and even mammals are not eaten frequently enough so that there is much chance of a snake taking two or more individuals at the same meal, unless it is robbing a nest containing a litter of young. [Illustration: Fig. 13. Diagram showing percentage frequency of occurrence of various categories of prey in a sample of 1008 food items identified from scats and stomachs of blue racers from the Reservation and Rockefeller Tract. Insects, especially, orthopterans, made up the great majority of prey items taken.]