482 



THE NATURE BOOK 



of frogs, in which period they are buried 

 in the mud, or under stones, often with 

 several feet of water above them, skin- 

 respiration is a 

 necessity. Dur- 

 ing his active 

 period a frog 

 breathes main- 

 ly, perhaps, by 

 his lungs, but 

 his skin, which 

 is moist and 

 delicate and 

 richly supplied 

 with venous 

 blood, has the 

 power of ex- 

 changing gases 

 in such a way 

 that he may be 

 said to breathe 

 by this also. 



The frog 

 being common 

 and easily cap- 

 tured, has had 

 the misfortune 

 to supply in 

 himself the cor- 

 piis vile for 

 i nnumerable 

 experiments. 

 Frogs have 

 been blinded to 

 determine the 

 reflex or volun- 

 tary character 

 of their colour-change, and frogs have 

 had their lungs removed to determine if 

 they could breathe without them. The 

 latter experiment showed that a frog 

 deprived of his lungs can live and 

 breathe for a considerable period. Let 

 us hope that human curiosity is for once 

 and all satisfied. 



In addition to breathing by his lungs 

 and external skin, the frog breathes by 

 the mucous membrane of his mouth cavity. 

 He may indeed be said to breathe with 

 every part of him which is exposed to the 

 external world. In certain tailed am- 

 phibians — the Itahan Salamandra perspi- 

 cillata, for example — not only are the gills 

 suppressed in the course of development, 

 but the lungs are suppressed also, and 

 it is supposed that, in these cases, the 



FRONT VIEW OF THE 

 BREAST BONES 



(SHOULDER GIRDLE) OF 



(1) THE COMMON TOAD, 



(2) THE GRASS FROG. 



That of the Common Toad is 

 of the arciferous type, in 

 which the bones and carti- 

 lages of the right side overlap 

 those of the left. That of 

 the Grass Frog is of the 

 firmisternous type, in which 

 the corresponding bones 

 and cartilages meet in a 

 straight line. 



1. Clavicle. 



2. Scapula. 



3. Glenoid cavity where the 



arm bone articulates. 



4. Coracoid. 



5. Supra-Scapula. 



6. Sternum. 



mucous membrane of the mouth is the 

 chief breathing organ. 



Sufficient reason for the complex breath- 

 ing in frogs and toads is supplied by the 

 fact that they have neither ribs nor 

 diaphragm. Their system of air supply 

 must therefore be entirely different from 

 our own. For a long time it was supposed 

 that the intermittent pumping action in 

 a frog's throat, accompanied by a pulsa- 

 tion (sometimes a heave) of the flanks, 

 was the action which supplied a frog's lungs 

 with air. Investigation has shown, how- 

 ever, that while this action takes place 

 the glottis (entrance of the passage to the 

 lungs) is closed, and that, consequently, 

 the action is not directly connected with 

 lung breathing. For a full explanation 

 of a frog's breathing mechanism, and for 

 a more detailed account of . a frog's 

 anatomy and life-history than it is possible 

 to embrace in this article, I would refer 

 the reader to Mr. O. H. Latter's excellent 

 little book, " The Natural History of some 

 Common Animals." 



Like the newts, frogs and toads possess 

 the power of regenerating lost appendages. 

 Tadpoles of both species will quickly 

 develop a new tail, or a new leg, to replace 

 a lost one, and the power is not wholly 

 lost in adults. Mr. Gadow gives an 

 instance of this limb-renewal in the case 

 of two Grass Frogs, each of whom had lost 



THE NATTERJACK TOAD. 



Distinguished by the yellow stripe down his back, the 

 practical absence of webbing on his feet, and his 

 mouse-like run. 



a hand at the wrist. Within a year both 

 had developed a four-cornered stump at 

 the end of the clean-cut limb, and two of 

 the pnjtuberances developed subsequently 

 to the length of four millimetres. 



