HARDWICKE'S SCIEN CE- GO S SIP. 



129 



over the case answers admirably for modulating the 

 light. By all meaus take care never to let the 

 least frost touch the plants, or they will never thrive- 

 J. S. William Durham, E.G.S. 



THE TORTOISE AND ITS SKELETON. 



THOSE who have never examined the bony frame- 

 work or envelope of a tortoise, can form no idea 

 of its complicated structure,of itswouderful mechan- 

 ism. In the living animal we see only the horny 

 plates, known as toitoise-shell, beautifully coloured 

 indeed and contrasted ; but remove these, which 

 fan be easily done after the animal is dead, and 



developed, and connected together by sutures. 

 The ribs, also developed into large and flat bones, 

 are attached to the margins of these processes, and 

 constitute the costo-sternal plates, representing the 

 sternal ribs of some saurians. 



The plastron, composed of nine pieces, has been 

 proved to be the sternum, of course highly de- 

 veloped. 



About a year ago I buried a favourite tortoise 

 which died on the approach of winter. I closely 

 sealed it in a wooden box in the garden, and have 

 lately exhumed it. A portion of the lid was broken 

 in, the work, no doubt, of some clumsy gardener, 

 and consequently a large amount of wet mould had 

 been washed in by the late rains : on attempting to 



Fig. ;o. Skeleton of Tortoise. 



putrefaction has accomplished its end, and the 

 wonderful sutured conformation of the upper and 

 lower shields strikes us at once with amazement. 

 These dove-tailed lines, which help to fasten the 

 bony plates that constitute the carapace and 

 plastron, must not be confounded with the indented 

 lines which correspond in size and shape to the 

 j)lates upon which these hitter rest. 



Physiologists inform us that the upper shield or 

 carapace is covered entirely by a skin ; attached to 

 which, probably by minute fibres, are the scales. 

 When the tortoise is dead and decomposition has 

 set in, the skin, to which the plates are attached, 

 is resolved into its constituent elements; the power 

 of cohesion is dissolved, the plates become loosened 

 and then easily separated. 



To the rest of the reptiles tortoises present an 

 anomaly; the broad osseous plates whicli extend 

 along the medial line of the carapace are supposed 

 by comparative anatomists to be the superior 

 spinous processes of the vertebral column, highly 



clean the remains, the whole fabric fell to pieces ! 

 Scales fell off, bony plates became detached, and all 

 that remained firm was the spinal column, which is 

 naturally consolidated to the vertebral plates. 



I was always under the impression that this 

 species, obtained from Leadenhall Market, was 

 Tedudo Graca, until it dawned upon me that in 

 that genus the sternum is immovable, whereas in 

 my specimen, the hinder part of the sternum could 

 be moved ; so I was forced to come to the con- 

 clusion that it is Chersina marginata, a species 

 which has often been confounded with the former, 

 and the posterior part of whose sternum is move- 

 able. 



The scales in general are yellow in the centre, 

 with radiating black, or rather dark brown, blotches 

 round the margin; in some scales the reverse occurs, 

 the centre being black. The shell, in my opinion, 

 is much prettier than its congeners, and differs 

 from it in general appearance. 



One cannot but be struck with the marginal 



