The Natural History of the Hog-nosed Snakes, Genus Heterodon: A Review'

ticularly as such studies contribute to other biological fields. Unfortunately much published information has been gathered uncritically, and is widely scattered through the literature. In an attempt to rectify these problems Fitch (1949) and Cagle (1953) have summarized what they believe should be included in life history studies. These reviews provide convenient forms for outlining facts regarding the life histories of reptiles. Even considering common species, available data fall far short of the ideals of Fitch and Cagle as is sharply demonstrated by the present review of the natural history of the hog-nosed snakes, genus Heterodon. Fitch's outline has been followed in this paper, although material of a biogeographic nature will be presented elsewhere. THE EGG AND EMBRYO Data on time of depositon, number and size of eggs of H. platyrhinos have been summarized in Table I. There may be a geographical influence on laying dates, as Logier (Ontario) and Breckenridge (Minnesota) report eggs laid in July, whereas in southern localities they are generally laid in June. August records involve captive snakes. Length of the ellipsoid, off-white, thin-shelled, non-adherent eggs varies from about 20 to 39 mm., and width from about 12 to 30 mm. Clark (1952b) measured volumes of two clutches by displacement of water; one clutch varied from 2.0 to 3.0 cc., mean 2.6 cc., and the other 3.5 to 5.0, mean 4.25 cc. Clark also shows positive correlation coefficients between length and width measurements on platyrhinos in contradistinction to Diadophis punctatus and Opheodrys vernalis which Blanchard showed to be negatively correlated. Clark's data are not entirely convincing as biases resulting from the many large and small eggs in his clutches would shift coefficients in a postive direction. Clark has shown also that volume is more closely correlated with length or width than they are with each other; this is to be expected as volume is a function of length and width in any body. Thus the correlations and the conclusions based upon them would appear spurious. Clutch size varies considerably; as few as four and as many as 61 eggs per clutch have been reported. Geographic variation in egg and clutch size is unknown. Data on the eggs of nasicus are rare. Breckenridge (1944) recorded a Minnesota specimen with 9 eggs. The most extensive information on