120 REPTILES AND BATRACHIANS 



rattle and rate of growth are made from this species and 

 also from others not found in the Palmer collection. 



At birth, the rattle is represented by a single button, 

 the basal piece. As the animal grows, this button is dis- 

 placed by another which has grown within it and crowded 

 it back, but which it now, being the first ring of the rattle, 

 clasps rather loosely. The new button is crowded back 

 in similar maimer by its successor, and so on, each seg- 

 ment of the rattle becoming a ring after a period of ser- 

 vice as a button. The ring which was the first button is 

 the smallest and is easily recognized by its shape : not hav- 

 ing been formed inside another, its angles and curves are 

 much less abrupt. Until a certain stage is passed, each 

 ring is smaller than that formed immediately after it. 

 Usually, from the first ring to the seventh, the rattle, as a 

 whole, is tapering; from the seventh, the rings are more 

 equal, and the edges of the organ are nearly or quite par- 

 allel. If the rattle is much tapered, it is evident that the 

 snake to which it belongs is comparatively young ; on the 

 other hand, if none but nearly equal rings are present, we 

 can only say the taper portion has been lost and that the age 

 of the snake includes sufficient time to form both the ta- 

 per and the parallel portions, with a possible addition for 

 lost rings of the latter. During the time of most rapid 

 growth the rings are most unequal ; those formed after- 

 ward make up the parallels. Consequently, the separa- 

 tion of the species, as advocated by some, into two groups, 

 one of which shall contain those with tapering, and the 

 other those with parallelogrammic rattles is an impossible 

 one. Of C. atrox, the young are less than ten inches in 

 length at the time of extrusion. Specimens on which the 

 first ring has appeared arc about double the length. Oth- 

 ers with a larger number of rings [trove that this rapid in- 

 crease is not kept up, but that year after year the rate 



