THE EDIBLE 1ROG. 353 



second day the sphere begins to elongate, and a groove, which had previously divided the upper part 

 into two, begins to close up, and the head becomes prominent, the tail begins to show itself, and 

 the little hooks, by which it subsequently lays hold of things, begin to appear. In somewhat more 

 than fifty hours the head becomes well marked, the membrane of the tail is seen, and the first 

 indications of branchiae occur on each side of the head. Moreover, the muscles of the spine may 

 be seen. The whole creature grows, and these parts become more distinct, and the branchiae consist 

 of two tubercles on each side, and as yet are undivided. The young creature now will give some 

 signs of voluntary movement, and the nostrils are seen, but the mouth is scarcely observable. 

 The eyes are just visible. The next stage is a division of the branchiaj into lobes, and the blood 

 may be seen circulating in them. The embryo is still restricted to a curved position by the 

 substance round it, and it may be seen to jerk itself about until it escapes. Bell says that 

 although all this may be done in the warm waters of the South of Europe, or in artificial water 

 at a temperature of 73 '4 Fahr. in four days, it takes at least a month in a colder climate. The 

 rest of the metamorphosis has been described in explaining the general peculiarities of the Amphibia 

 (p. 348). When the metamorphosis is completed, and the little Frog has received its permanent shape, 

 the skin gradually becomes coloured, and, according to the light, the prevailing colours of the surround- 

 ing objects, the health of the creature, and possibly from nervous influences, the tints change, the mobility 

 of the colour corpuscles within the skin being the cause. It appears that the skin of the Frog, when 

 kept damp, plays an important part in the elimination of carbonic acid gas, and also in the absorp- 

 tion of oxygen from water, and probably from air; for experiments have shown that the lungs 

 are not sufficient to carry out the respiratory process perfectly, so that the skin must be utilised. 

 Bell believes that during the damp condition of the skin water is absorbed and stored in a sac 

 which acts as if it were a urinary bladder. This store he considers is kept to moisten the skin 

 when it requires it for the purpose of respiration. It is re-absorbed and deposited in the skin. 



In vertebrate animals the bones may be formed with a groundwork of cartilage, in which 

 osseous grains are gradually deposited, and such are cartilage bones. Others have no cartilage, but the 

 bone is deposited in a membranous tissue, and such are membrane bones, of which the parietal or 

 frontal bones of the mammalia are examples. Huxley states that in the higher vertebrates the 

 cartilage bones rarely remain as such, but the ossified cartilage becomes absorbed and is replaced by a 

 membrane bone derived from the investing tissue. 



The Frog's skull is characterised by a cartilage bone called by Cuvier the os en ceinture, or 

 girdle-bone. " It is an ossification which invades the whole circumference of the cranium in. the 

 pre-sphenoidal and ethmoidal regions, and eventually assumes somewhat the form of a dice-box, 

 with one-half of its cavity divided by a longitudinal partition. The septum and the front and 

 back halves of the bone correspond to the ethmoid pre-f rentals, and the orbito sphenoids of the other 

 vertebrata." (Huxley.) 



The Edible Frog,* found and used as an article of food in many parts of the Continent, is 

 also an inhabitant of England. It can be readily distinguished by the absence of the large 

 distinct black mark on the side of the head to the shoulder, seen in the Common Frog, and by the 

 presence of a light-coloured line running down the back, and by its marking with round circumscribed 

 spots. The thumb has two large tubercles on it in the male, whose vocal sacs are large and globular. 

 Mr. Bond found them in Foulmere Fen, Cambridgeshire, and observed that their croaking was dif- 

 ferent from that of the Common Frog, the sound being like a loud snore. It is a timid animal, disap- 

 pearing on the least alarm, seems to come rarely, if ever, to land, and is essentially a dweller in the 

 water. It inhabits running or still watei-s, rivers, streams, lakes, ponds, salt or fresh marshes, and 

 even ditches, and it may be seen sunning itself on a water-lily leaf, and rarely on the banks. The 

 slightest noise alarms them, and they rush to the water. Their remarkable croak has procured them the 

 title of Cambridge Nightingales. When this is going on the male blows out his sacs, which appear on 

 each side of the head. This description holds good for the Continental Esculent Frogs. The hind legs 

 are the parts which are to be cooked, and in spite of some folk's antipathy, there is no doubt that they 

 are very nice when well cooked and served, for they taste like the most delicate spring chicken. 



The genus Rana is well developed in America, and the American Bull Frog is well known (Rana 



* Rana csculenta. 



