TORTOISES AND TURTLES. 25 



at last they came to lie, as we see, entirely 

 within the shell. 



It is interesting to note that some few tor- 

 toises seem to have found that the inflexible 

 bony shell, such as we have just described, 

 needed yet further modification to make it a 

 thoroughly trustworthy fortress against attack. 

 This need has been met by developing a hinge 

 either across the carapace, or across the plastron 

 or breast shield. By this means one or other or 

 both of the apertures of the shell can be closed 

 completely as by a portcullis. The hinged 

 carapace, be it noted, is found only in these 

 species belonging to the genus Cinyxis, found in 

 tropical Africa, whilst the hinged plastron has 

 been independently acquired by several different 

 tortoises in widely different parts of the world. 

 Thus the little Spider-tortoise of Madagascar has 

 the plastron so hinged that the front portion can 

 be drawn up, so as to completely close the mouth 

 of the shell. The Iberian tortoise of Spain and 

 Morocco closes the hinder aperture of the shell 

 in a similar manner. In this species, however, 

 the hinge does not appear till comparatively late 

 in life, and is best developed in females. Some 

 six species of the genus Testudo, found in India, 

 Madagascar, and S. China, can also .close this end 

 of the shell by raising the hinder half of the 

 plastron. But the N. American species of the 

 genus Cistudo have made a decided improvement 

 on the mechanism adopted by the foregoing, 

 inasmuch as these can raise both ends of the 

 plastron, so that when the head, legs and tail 

 are drawn in, and the "oak is sported," the 



