1934 The Zoologist— Decembek, 1869, 



On the metamorphosis of frogs, however, M. Qiiatrefages stands pre- 

 eminent, and his observations are so immeasurably superior to ray 

 own that 1 shall copy from Dr. Lawson's translation. 



" The development of frogs presents another curious phenomenon. 

 It is this : the young animal, after it has left the egg, and before it has 

 becouje a larva, is still in a semi-embryonic condition : at this period 

 the digestive lube and its appendages are exceedingly rudimentary. 

 The greater portion of the body is filled by a large mass of yelk or 

 vitellus, enclosed by the skin, which has been formed for some time ; 

 and it is at the expense of this alimentary matter that the develop- 

 ment proceeds. The external characters are in keeping with the im- 

 perfect condition of the animal at that period : the head is large and 

 appears to be divided in two on the under surface, each half being 

 prolonged as a sort of process by which the animal attaches itself to 

 surrounding objects ; as yet there are no traces of either eyes, nostrils, 

 respiratory or auditory organs ; and the belly, of an oblong form, is 

 continued posteriorly as a short tail bordered with a ribband-like 

 membrane. This primitive condition, however, does not last long. 

 About the fourth day after birth the head, which is now as long as 

 the body, has somewhat the appearance of a thimble ; the mouth is 

 provided with a pair of soft lips ; the nostrils, eyes and auditory ap- 

 ])aratiis have made their appearance ; the head is separated by a deep 

 groove from the belly, which has assumed a spherical form, and from 

 which spring a pair of opercula, clothed with little branching gills; 

 and the tail has grown so much that it is now quite as large as the 

 body. Tlie mouth is very soon armed with a horny beak, capable of 

 dividing the vegetable food; the intestine, which is now very long, 

 becomes more fully formed and assumes a spiral arrangement; the 

 tail is elongated and widened, and the little creature is then called a 

 tadpole. At this period one of those alterations occurs which are so 

 intimately associated with the ideas we are endeavouring to convey, 

 that we must not pass them by in silence. Our larva first breathed by 

 its skin alone, and afterwards by a pair of little branching gills 

 attached to the opercula: about the seventh or eighth day, however, 

 the opercula are gradually soldered to the abdomen, and the gills 

 fade away and disappear. At the same time a set of new and more 

 complex branchia are developed, in chambers situate on either side 

 of the neck. The new gills are arranged in tufts attached to a solid 

 frame-work of four cartilaginous arches, and are about a hundred and 

 twelve in number for each side of the body. Here we see a rapid 



