92 SATURDAY LECTURES. 



water. In some crabs belonging to the genus Porcellana 

 the anterior spine or rostrum is supple, and many times 

 longer than the body. After a few months the form changes 

 material!}', the month-parts, which before were swimming 

 legs, are now fitted for i)reparing the food, and we have 

 what is known as the Megalops condition, which looks much 

 like a lobster, but in which the mature crab is sufficiently 

 foreshadowed. (Fig. 6.) 



Let us now leave the ocean and talk of a few of the com- 

 moner animals inland. 



THE FROG. 



The common frog, {Rana temporaria,) which occurs both 

 here and in Europe, passes the winter buried in the mud of 

 stagnant waters, in a torpid condition; aye, and it may even 

 be frozen till it is so brittle as to chink, without the loss of 

 life. The frogs are now issuing forth to join with their pe- 

 culiar croak in the zoological concert of spring. The ac- 

 companying figures will aid us in understanding the trans- 

 formations of the frog. They are poor coj)ies of the admira- 

 ble originals of Roesel von Rosenhof, generally credited to 

 Mivart, because this last author failed to credit them to the 

 proper source. Hatching from dark globular eggs enclosed 

 in a transparent, gelatinous fluid which agglutinates them 

 and enables them to float in masses on the water, the young 

 tadpole congregates under the leaf of some aquatic plant, 

 where it feeds by suction. It has prominent external 

 branchiae, and is in every respect admirabl}^ adapted to 

 aquatic life. The legs are firsl seen as mere buds, the front 

 pair hidden under the 02:)ercular membrane. As they de- 

 velop the gills are absorbed ; the mouth loses its suctorial 

 character; the e3'es, instead of being concealed, become ex- 

 posed, and the front limbs are uncovered. The tail is next 

 gradually absorbed, and the animal is now truly amphibi- 

 ous, for the lungs, Avhich have replaced the gills, enables it 

 to live out of water. From a vegetarian it has become car- 

 nivorous and now comes on land in search of worms and 



