FROGS AND THEIR USES. 183 



that the frog is devoid of any neck ; that its spine makes a hump 

 near the middle of its back ; the characters of its two pairs of 

 limbs ; and other external features, are all too well known to the 

 intelligent observer and reader to require special description here. 

 There is another thing we must notice, however, and its pres- 

 ence is not generally observed, nor appreciated. If we watch 

 carefully at the distal end of the backbone, upon either side of it, 

 it will be seen that the skin pulsates at those points with sufficient 

 force to make it apparent to the eye. These pulsations are per- 

 formed by the posterior pair of lymph hearts. Now, the lymph 

 hearts have nothing to do with the circulation of the blood as 

 performed by the heart, but they, on the other hand, pump the 

 lymph contained in the large lymphatic vessels into the veins. 

 There are two pairs of these lymph hearts the pair just noticed 

 and an anterior pair, which are below the margin of the shoulder 

 blade, upon either side, and near the lateral processes of the third 

 vertebra. They are muscular organs endowed with the power of 

 contraction, and are extremely important ones in the internal 

 economy of the frog. 



In a brief essay, such as I am now writing, it will by no means 

 be practicable to enter upon the extremely interesting subject 

 of the internal structure of the frog. Even to touch upon this 

 ever so lightly would require a small volume to print it. Not a 

 few books are in circulation now devoted largely to the anatomy 

 of these animals, and others no doubt will appear from time to 

 time. A few years ago the distinguished British naturalist, Prof. 

 St. George Mivart, devoted an entire treatise to The Common 

 Frog, and it is truly a most instructive work. In it he describes a 

 number of different kinds of frogs, but what gives the book its 

 special biological significance is that he discusses the life history 

 of these tailless batrachians, and their anatomy and physiology, 

 with a variety of other forms that are either closely affined to 

 them or more or less remotely connected. In summing iip, Prof. 

 Mivart shows the differences existing between a frog and a fish, 

 a frog and a reptile, a frog and a bird, a mammal, and so on ; and 

 indeed what a frog really is, and he claims it to be " a tailless, 

 lung-breathing, branchiate vertebrate, with four limbs typically 

 differentiated, undergoing a complete metamorphosis, and pro- 

 vided with teeth along the margins of the upper jaw." This last 

 character is one that distinguishes the frogs from the toads, while 

 from other batrachians the frogs are at once separated by the ab- 

 sence of a tail. 



In the United States we have at least fifty or sixty different 

 species and subspecies of frogs and tree frogs, belonging to a 

 number of different genera. The typical genus is Che genus Rana, 

 and to it belongs our common bullfrog (Rana Catesbiana), it at 



