192 REPTILES AND BATRACHIANS 



in all young Batrachlans. Strong, horny tubercles are 

 frequently present, especially in the case of the burrowing 

 Anura, on the base of the inner toe. Besides four fingers, 

 a rudiment of thumb is almost constant in the Tailless 

 Batrachians. In the male of some frogs, such as Rana 

 holsti and Hyla maxima, what at first sight appears to 

 be an innocent rudiment of the thumb, is in reality a 

 very formidable weapon, for mounted upon the carpus is 

 a long, sharply pointed bone, which pierces the skin when 

 pressure is made upon it, and when one of these frogs is 

 caught it invariably strives to insert the spurs into the 

 hand that holds it. Some Tree-Frogs {Hyla) are similarly 

 remarkable for possessing spine-like processes on the front 

 of the arms, and the inner fingers and the breast of some 

 South American Leptodactylus are armed, during the 

 breeding season, with very powerful horny spines. 



The skin of all Batrachians is studded with glands, 

 which, in most toads, form large warts on the body, and 

 are aggregated on each side of the head, behind the eyes, 

 to form a large glandular mass, known as the parotoid 

 gland. These secrete a milky, poisonous fluid, which is 

 exuded when the animal is molested, sometimes to a 

 considerable distance, and which serves as a protection 

 against most mammals. Many snakes feed on both frogs 

 and toads, not having, with a few exceptions, any repulsion 

 for the poison. Even species with a perfectly smooth skin 

 may be highly poisonous, the skin of our European Tree 

 Frog, Hyla arborea, for example, being endowed with great 

 toxic properties. The secretion of the frog Dendrobates 

 tinctorius is employed by the Indians of Colombia for 

 poisoning their arrows, the poison being obtained by ex- 



