STRUCTURE OF SERPENTS AND BATRACHIA. 97 



gullet, oe, which leads from the mouth to the stomach, is a 

 long and very wide canal, being even larger than the stomach 

 at its commencement ; a portion of it is removed at oe', in. 

 order to show the heart, &c., which would otherwise be con- 

 cealed by it. The stomach, i, is long and narrow ; and the 

 intestinal tube, i', after making a few turns or convolutions, 

 passes backwards in a straight line, to terminate in the cloaca, 

 cl, which opens externally by the orifice, an. The liver, /, is 

 also much lengthened. From the mouth also proceeds the 

 long windpipe, t t, which conveys air to the lungs, or rather 

 to the single lung ; for the lung on the left side, p' } is scarcely 

 at all developed, whilst that on the right, p, extends along a 

 great part of the body. At o is seen the ovarium, in which 

 the eggs, o' o', are produced ; and this also is very much 

 lengthened, extending from the cloaca a good way up the 

 body, so as nearly to meet the lung. The other references 

 are to the parts of the heart, and the principal vessels ; the 

 structure and arrangement of which will be explained here- 

 after ( 284). 



86. The Batrachia, or animals of the Frog tribe, are 

 readily distinguished from all the preceding, by their soft 

 naked skins ; even when the form of the body, as in the com- 

 mon Salamander or Water-Newt, resembles that of the lizards. 

 They are also remarkable for the metamorphosis which they 

 undergo in the early part of their lives ; for they come forth 

 from the egg in a condition which is, in all essential particu- 

 lars, that of a fish, and undergo a gradual series of changes, 

 by which their form and structure become assimilated to those 

 of the true reptiles. This change is most complete in the 

 Frogs and Toads ; the early form of which is known as the 

 tadpole. The principal stages of this change are represented 

 in figs. 35 to 39 ; in which, however, the relative sizes are 

 not preserved, the tadpoles being much larger in proportion 

 (for the sake of displaying their form and the gradual 

 development of their legs) than the complete frog. Soon 

 after the young tadpole has come forth from the egg, it pre- 

 sents the form which is shown in fig. 35 ; its head and 

 trunk are large, and the latter is prolonged into a flattened 

 tail, by which the little animal swims freely through the 

 water. There is not the least appearance of limbs or mem- 

 bers. It breathes by gills, which are long fringes, hanging 



H 



