566 ANATOMY OF VERTEBRATES. 



the carotids, and divides to accompany them a short distance. In 

 the young Crocodile' the thymus is relatively larger, thicker, 

 subtrihedral, extending backward upon the pericardium, as well 

 as forward along the carotids to the basis cranii. In young 

 Chelonia an elongate body, of a yellowish white colour, lies 

 between the carotid and axillary trunks on each side : it presents 

 lateral cavities, defined by limitary membrane, and containing 

 nuclei, oil-drops, and fine molecular matter. In older Chelonia it 

 seems to degenerate into fat. 



§ 105. Reproducible Parts in Ilcamatocrya. — One effect of life 

 is the reproduction of the parts of the body as they pass away 

 through unfitness for the required actions : this mainly takes 

 place molecularly and invisibl}' ; but parts of the integument, hairs, 

 teeth, antlers, may be cast off en masse, and reproduced on a scale 

 which catches the ordinary attention as a new growth. Certain 

 animals have the fxculty of reproducing organs and compound 

 parts of the body which may have been removed by violence : 

 amongst Vertebrates the property is greatest in the cold-blooded 

 series ; and here, so far as experiment yet shows, is most conspi- 

 cuous in the tailed species and larvas of the batrachian order. In 

 the JS^ewt ( Triton) the tail, amputated at any distance from the 

 base, is reproduced : the same with respect to the fore-limb and 

 hind-limb, the reproduced member having the digits, but with 

 diminished j)ower of movement. The same member has been, in 

 young Newts, removed and restored four times successively. In 

 the experiments recorded by Bonnet,^ it was found that warmth 

 promoted, and cold retarded, the regeneration of the part. An 

 eyeball of a Newt was extirpated, and, in the course of a year, it 

 was restored with the usual organisation. Dumeril cut off about 

 three-fourths of the head of a Triton marmoratus, and deposited 

 the animal at the bottom of a large vessel, having half an inch 

 depth of water, which was constantly renewed. The Newt con- 

 tinued to live, and to move slowly. The nostrils, the tongue, the 

 eyes, and the ears were gone, and the senses reduced to that of 

 touch. It crept slowly, and Dumeril imagines cautiously, about, 

 occasionally raising the neck to the surlacc, as if to breathe. The 

 process of cicatrisation at length completely closed the aperture of 

 respiration and deglutition ; and so it survived for three months 

 after the operation, when it died from accidental neglect. This 

 experiment exemplifies chiefly the power of endurance of mutila- 

 tion, and, collaterally, the respiratory function of the skin. In 



' I Iiavc not liad an opportunily of examining this structuic in a full-grown speci- 

 men of Crocodilian. ' coci. torn. xi. pp. G2-179, 



