SNAKES OF THE GENUS PITUOPHIS 



11 



The food is varied, althougli quite uniform throughout the genus. 

 The major part consists of small mammals, especially such rodents as 

 pocket gophers, rats, mice, ground squirrels, and yoimg rabbits, but 

 also occasionally includes birds, eggs, lizards, and even other snakes. 

 The prey is constricted and swallowed whole, or, if it is small and 

 weak, may be taken alive without constriction. 



Most of the forms are known to be oviparous, and the remaining 

 ones are undoubtedly so. At the time of deposition the eggs contain 



210-4 215-9 220-4 225-9 230-4 



Figure 7.— Soxual variation in the number of ventrals in 72 specimens of Pituophis c. catenifer from the 



vicinity of Palo Alto, Calif. 



embryos, which are fairly well developed in all the forms that have 

 been studied. What few records we have of breeding habits are 

 included under the descriptions of the forms to which they pertain. 



Variation. — The phylogenetic relationships of the forms within a 

 genus can be understood only from a thorough study of the variation — 

 individual, sexual, and geographic — found within each form. Among 

 the various forms of a genus the variability of a given character may 

 differ greatly in degree as well as kind. Thus, in one form the geo- 

 graphic variation in a certain character may be marked, even though 

 the individual variation in any given part of the range may be very 



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