PRAIRIE RATTLESNAKE. 673 



explained by supposing that the venom accumulates owing to the fangs 

 being shed. 



Various theories have been advanced as to the use of the rattle, 

 none of them being entirely satisfactory. One supposition is that it has 

 resulted in time from the agitation of the highly nervous tail, and has 

 no special function. Pityophis melanoleucus, the Bull Snake shows such 

 an agitation, and its tail when in motion is said to somewhat resemble 

 the rattle of this Bpecies. Again, it has been conjectured to be of use in 

 calling the sexes together, and thus aiding in the preservation of the 

 species. Another hypothesis is that, as it resembles the noise made by 

 a grasshopper, it might be of service in decoying insectivorous birds 

 within reach of the animal. The rattle is said to be heard often when 

 there is no cause of irritation. If such be the case, it probably does not 

 occur with the Orotalidae in our limits. A fourth suggestion is that it 

 serves to alarm the higher species, giving them warning, and thus en- 

 abling them to escape its bite. Such a hypothesis is contrary to all 

 analogy, since nature's mode is to provide the animal with that which 

 is best for its individual wants without regard to others. A last supposi- 

 tion is that it is of use to the serpent in terrifying its enemies. Proba- 

 bly this last is more worthy of credence, and is not to be set aside by 

 the fact that it sometimes attracts the attention of enemies in such a 

 way as to induce them to destroy it. In other cases it renders the 

 snake more frightful, and enables it to paralyze its foes or desired prey 

 with fear. It may also be of some use in the other ways mentioned, 

 especially in bringing about the union of the sexes. 



A popular belief is that one rattle is added each year; however, this 

 cannot be true, as Dr. Holbrook knew a case of two rattles being added 

 in a year, and Dr. Bachman observed a species in which four were 

 developed in twelve months. Thus, we may see that the number of rat- 

 tles is, as Dr. Holbrook observed, dependent upon the condition of the 

 animal as regards liberty, nourishment, etc., and is no test of age. 



The oil of this species is said to be very valuable. 



Gends CEOTALOPHORUS. Linuajus. 



Cephalio region above covered with plates, whicli are seen posterior to a transverse line 

 between the eyes ; caudal rattle always present, though smaller than in Crotalus ; body 

 iBoderately strong; pupil vertical ; rostral plate moderately large, temporals and labials 

 'Small ; the two anterior inframaxillaries large, the remaioder small. 



Dorsal rows of scales 26. . . • C. tbegsminus. 



Dorsal rows of scales 23 C. miliarius. 



43 



