. Outlines of zoology. ttained. Lungs are always developed in theadults. ? It is doubtful whetherthey are directly comparable withthe swim-bladder. The heart has three chambers. Thereis an inferior vena cava, and pairedposterior cardinals are seen only inthe larva. The limbs have digits. There are no fin-rays. There are two occipital condyles. Acolumella runs from the tympanumto a fenestra ovalis in the earcapsule. There is no exoskeleton, except in afew cases, and in extinct forms. There are posterior nares opening intothe cavity of the mouth. The cloacal bladder seems to be thehomologue of t
. Outlines of zoology. ttained. Lungs are always developed in theadults. ? It is doubtful whetherthey are directly comparable withthe swim-bladder. The heart has three chambers. Thereis an inferior vena cava, and pairedposterior cardinals are seen only inthe larva. The limbs have digits. There are no fin-rays. There are two occipital condyles. Acolumella runs from the tympanumto a fenestra ovalis in the earcapsule. There is no exoskeleton, except in afew cases, and in extinct forms. There are posterior nares opening intothe cavity of the mouth. The cloacal bladder seems to be thehomologue of the allantois s8o AMPHIBIA. The Frog as a type of Amphibians The common British frog (Rana temporarid) and thefrequently imported continental species {R. esculentd) agreein essential features. Though aquatic in youth, they often live in dry places,hiding in great drought, reappearing when the rain one knows how they sit with humped back, how theyleap, how they swim. They feed on living insects and Fig. 312,—The edible frog {Rana esculenta). These are caught by the large viscid tongue, which, beingfixed in front of the mouth and free behind, can be jerkedout to some distance, and with even greater rapidity re-tracted. When a frog is breathing, the nostrils are alternatelyopened and closed, the under side of the throat isrhythmically expanded and compressed, the mouth re-mains shut meanwhile. The males trumpet in theearly spring to their feebly responsive mates. In ourBritish species the pairing takes place soon after; theyoung are familiarly known as tadpoles, and a notablemetamorphosis takes place. In winter the frogs hiber- THR FROG %%\ nate—buried in the mud of the ditches and ponds, mouthshut, nose shut, eyes shut—and breathe through their skin. Form and external features.—The absence of neck andtail, the short fore-limbs almost without thumbs, the longerhind-limbs with five webbed nailless toes and with a longankle region, the apparent hump-back
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
