THE AMERICAN NATURALIST [Vol. XLVII 



than one body vertebra and belly scale more and between 

 five and seven caudal vertebrae and subcaudal scales less 

 in the females than in the males. 



3. There is considerable variation in the total num- 

 ber of vertebrae and scales in the two sexes, variations in 

 the series of one member rarely equaling opposite varia- 

 tions in the series of the other. 



It goes without saying that the extent of variation in 

 the two series is probably not indicated in the small 

 amount of material used, but the relations of the num- 

 bers in the different series are so little variable that 

 there can be but little doubt that the above summary ex- 

 presses the general conditions. 



It is not known at present just how widespread this 

 close correspondence in the number of vertebrae and ven- 

 tral scutes is among snakes, but it is conservative to say 

 that there is probably a correlation between the two 

 series in most, if not all, forms, and that in some groups 

 this correlation approaches close correspondence in the 

 number of parts. It follows from this that, as in R. 

 leberis and R. grahami, the species with most numerous 

 ventral scales have more vertebrae than others in which 

 the same correspondence prevails, and the opposite, and, 

 as the senior writer has shown that variations in size in 

 groups of related species in the genus Thamnophis are 

 associated with differences in the number of scutes, the 

 larger forms having more scales than the smaller, it may 

 be assumed, tentatively at least, that difference in rela- 

 tive size in such a group of closely related species is a 

 deep-seated modification that affects the number as well 

 as the size of the metameres. 



LITERATURE 



Bateson, William. 1894. Materials for the Study of Variations. London. 

 Gadow, Hans. 1901. The Cambridge Natural History, Amphibia and Rep- 



Zeitsch. /. Wissensch. Zool, LXXX, pp. 56-79. 

 Jourdran, E. 1903. Les Ophidiens de Madagascar. Paris. (Thesis.) 



