30 BULLETIN 160, UNITED STATES NATIONAL MUSEUM 



of B. compactilis and B. simus, often materially changes the general 

 appearance of the species. Nieden, in his key to the genus Bufo, 

 often uses the occurrence of single or double subarticular tubercles 

 on the toes as a diagnostic character. In many instances the number 

 of subarticular tubercles present at each joint varies from one to two 

 on the same digit, and 3^et the number of such tubercles will be con- 

 stant in the majority of the specimens in any large series. 



Although most kinds of toads are squat, fat, and warty, there are 

 some smooth-skinned species, one of wliich {Bvfo alvarius) inhabits 

 the arid sections of Southwestern United States and northwestern 

 Mexico. There is also a slender-bodied tropical toad {B. haematiticus) 

 that reminds one of a frog. Of the many kinds of toads living to-day 

 in different parts of the world, both the largest and the smallest 

 belong to the American fauna. The largest, B. marinus, ranges from 

 northern Mexico southward to Patagonia, and within the United 

 States and northwestern Mexico is a form nearly as large, which is 

 locally known as the Colorado River toad {B. alvarius). Large 

 individuals of B. marinus mfij have a body length of 9 inches and a 

 mouth large enough to swallow small birds, but insects constitute the 

 major portion of their food. Probably the smallest living toad is the 

 oak toad, B. quercicus, of the Southeastern United States; this species 

 feeds largely on ants. The little green toad, B. debilis, is the smallest 

 Mexican member of the genus. 



Most toads have the skin covered with warts, which are more 

 closely aggregated on the sides of the neck than elsewhere, and these, 

 together with a pair of large glandular masses, the parotoid glands, 

 situated behind the eyes, secrete a milky poisonous fluid whenever 

 the animal is molested. This secretion is an acrid irritant, causing 

 pain in cuts and producing a bitter astringent sensation in the mouth. 

 Some investigators have advanced the idea that the female lacks this 

 fluid during the breeding season, while the male at the same time 

 has an overabundant supply of it. 



According to Madame Phisalix, toads possess two distinct kinds of 

 glands, which secrete venom of different properties, one type pro- 

 ducing a mucous and the other a granular venom. While the mucous 

 glands are distributed over the entire body, they are principally 

 found on the abdomen. The mucous secretion produced is an alka- 

 loid that acts as a narcotic, its effect being confined to the nerve 

 centers. Glands situated on the back, together with the parotoid 

 glands on the shoulders and connected with them, secrete a granular 

 acid venom that acts as a convulsive. 



It is not unusual to find hundreds of toads belonging to the same 

 species congregated in a small pond, temporary pool, or shallow 

 stream during the breeding season. Some species are far less numer- 

 ous, and a dozen pairs may comprise the breeding population for 



