NOTE-BOOK OF A NATURALIST. 259 



The old nursery-book told us, and told us truly, under 

 usual circumstances, that 



The tortoise securely from danger does dwell. 

 When he tucks up his head and his tail in his shell. 



The true Terrapenes, or, as those land-tortoises are 

 called by Jack, ' Turpins,' may defy the general chapter 

 of accidents, though there may be no safety either for 

 him or the poet, on whose bald head a raptorial bird 

 may drop the reptile from on high, taking the calvarium 

 for a stone. With a dorsal buckler, constructed princi- 

 pally out of eight pairs of ribs, united towards their 

 middle by a succession of angular plates, into which the 

 ribs are, as it were, inlaid ; and a plastron or breastplate 

 composed of nine pieces, each of which, with one excep- 

 tion, are pairs, the ninth being placed between the four 

 anterior pieces, with the two first of which it generally 

 coheres, when it is not articulated with the four, and the 

 whole forming in the adult a strong breast-and-belly 

 plate — compact in all its parts, and united on each side 

 to the dorsal buckler, the whole being so framed and 

 composed as to resist a very high degree of pressure, or 

 a powerful blow, — the land-tortoise has only to offer the 

 passive resistance of its defensive armour to set at nought 

 the attacks of ordinary enemies. There is one genus of 

 land-tortoises * which does not grow to such a size, or 

 carry such ponderous armour, as those of the genus Tes- 

 tudo, that has a still farther safeguard against the preda- 

 tory animals to whose attempts it is exposed. In this 

 form the anterior portion of the plastron, reaching back- 

 ward to the space occupied by the two first 23airs of 

 sternal plates, is susceptible of motion. Under the 

 strongly-marked suture of the second with the third 

 pair, is the elastic ligament which serves for a hinge. 

 When the animal wishes to open this moveable lid, uncler 



Pyxis. 



