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BATRACHIA. 



which, like the frog 1 , appear *n more states than one, 

 there must be a general use in nature for each state. 

 The egg, the tadpolf:, and the perfect frog, must all 

 have their part to perform a purpose which they 

 answer, besides keeping up the succession. 



And this natural use of the creatures is twofold : 

 they are useful in that which they consume, and in 

 that by which they are consumed ; and if there is a 

 change of state, both uses change along with it. The 

 same insect, as an egg feeds the titmouse in early 

 spring:, the warbling songster as a caterpillar in sum- 

 mer, and the bat as a moth in the full heat of the 

 season. It is probable that, but for the tadpoles, 

 the ponds and ditches which they inhabit would, 

 against the torrid season, become rank to pestilence 

 with the remains of small life. But while they are 

 performing this operation, and it is far from an unim- 

 portant one, they are preparing the surplus of their 

 own abundant array as subsistence for another race 

 of feeders. The ducks, and all the other birds which 

 nestle in the marshes or on the banks, and dabble for 

 their food in the shallow waters, would, in many in- 

 stances, fare but scantily, if the spawn of the frogs 

 did not supply them in the early season, and the tad- 

 poles when it is more advanced. Thus the abundance 

 of these creatures in their early stages is not a waste, 

 but a wise provision for other races ; and if they were 

 struck out, the blank which would thereby be occa- 

 sioned in nature would be much greater than one 

 would at first consideration suppose. Indeed, where 

 drainage and culture have taken away the nursing 

 places of the batrachia, the marsh birds also have 

 departed ; and there is no question that the one is, to 

 a certain extent, the cause of the other., 



And when they are full grown they still have their 

 double use. In the water, or upon land, they restrain 

 the superabundance of insect life under circumstances 

 that do not readily admit of its being done by races 

 differently formed. The leap, which is the prominent 

 motion of the frog?, and which all the four-footed por- 

 tion of the race can perform, is a motion of capture, 

 as well as of mere progression. The habit varies, and 

 some have more the character of liers in wait ; but 

 still they are all fitted for keeping within bounds the 

 exuberance of something, which could not be so well 

 kept down by creatures differently formed. 



That over which they are thus set is seasonal, and 

 also^ occasional, so that they hybernate at those 

 times when the economy of nature does not require 

 their action ; and at other times they can endure the 

 want of food long and patiently to a degree which 

 is utterly incompatible with the nature of animals 

 having more ardent systems. All reptiles have this 

 enduring quality to a very considerable extent ; and 

 on that account they may be called Nature's " extra- 

 ordinary labourers." They remain torpid and quiescent 

 till the season which requires them comes round, and 

 then they are ready, and in action in an instant. One 

 knows not whether most to admire, the perpetual 

 activity of some other races of animals, or the perfect 

 obedience to their time, which is displayed in these. 

 In form and habit they are different, but in purpose 

 and adaptation the one is every way as admirable as 

 the other. 



When the appointed season, during which the dif- 

 ferent species of the batrachia are to remain in their 

 aquatic state as breathers of water, draws to a close, 

 they undergo those changes, both of external and of 

 internal structure, which are to fit them for their new 



state. But the development of the new parts rather 

 precedes the shedding or absorption of the old ones. 

 Tadpoles may be seen, with the feet pretty well de- 

 veloped, and the swimming tail still adhering; and 

 there is also one period of their lives, however short, 

 in which both set* of breathing apparatus can act. 

 When the lungs asotimethe superiority, the characters 

 of the laud animal predominate throughout the whole 

 structure ; but in those genera in which the gills con- 

 tinue, the characters of the aquatic animal continue 

 predominant. Light is, however, essential to the change. 



The three genera which retain the double function 

 in breathing arc, the siren, protcus, and menobranclntx. 

 They are all inhabitants of the water ; and hitherto 

 they have been found only in America. Their eco- 

 nomy in a state of nature is but imperfectly under- 

 stood ; and it is doubtful whether they use both 

 systems either at the same time, or alternately with 

 each other. They are very curious creatures, how- 

 ever ; and the little that is known of each of them 

 will be stated under the generic names. 



The system of circulation in the batrachia bears 

 some resemblance to that of the other reptiles, and also 

 to that of the fishes. Red blood circulates to the 

 remotest parts, though slowly, and in but small quan- 

 tity ; and the web of a frog's foot, in consequence of 

 the transparency of the integument, and the slowness 

 of the circulation, is one of the very best cases in 

 which to observe the passage of the blood from the 

 arteries to the veins, and thus establish that the grand 

 mass which flows through the system is the same, 

 however it may, in successive portions, be altered 

 by substances with which it parts or takes up. 



To observe the living tide at this "turn" of its 

 course, when it has communicated all the nourish- 

 ment which, at that passage over the body, it is 

 capable of communicating, and when it is about to 

 return, taking up the absorbed surplus and the pre- 

 pared food on its way, is one of the most interesting 

 points in the animal economy ; but it is one which is 

 very difficult to be seen, more especially in animals 

 that have a quick circulation. Artery and vein never 

 anastomose with each other ; and, except through the 

 heart, or that which answers the same purpose, they 

 have no communication but through those capillary 

 junctions, which are so small that they are not visible to 

 the naked eye. It docs not even appearthat they bleed 

 when lacerated ; for the blood which is obtained from 

 a wound is either arterial or venous, and never the 

 intermediate blood of the capillary. This increases 

 the interest which is felt in observing the living 

 action ; but that action cannot be seen without the 

 aid of a microscope of high power, and that power 

 of course multiplies the velocity as much as the 

 lineal dimensions. 



While the batrachia are in the tadpole or gilled 

 state, the system of circulation is exactly that of a 

 fish. The heart has but one auricle and one ventricle. 

 The aorta proceeding from the latter divides into as 

 many branches as there are gills, and thence it returns 

 by veins to an arterial trunk situated on the spine. 

 From this trunk the systematic arteries are ramified 

 over the body, and from their extremities the veins 

 originate, and bring back the returning blood to the 

 auricle. Thus the heart of the tadpole is only a 

 branchial heart, sending the blood to the gills by its 

 contractions, and the systematic circulation is per- 

 formed by the arteries alone There is thus little or 

 no force o* velocity in the systematic circulation, and 



