REPTILIA. 391 



young in confinement, but it is doubtful whether they do so under natural 

 conditions. The female Python disposes herself in coils round her eggs and 

 incubates them for a prolonged period. During this process the tempera- 

 ture has been observed to rise as high as 96 F. within the coils \ 



Many Lizards possess the power of casting off and of reproducing 

 portions of the tail. The Reptilia pass into a lethargic condition in winter, 

 where the cold reaches a sufficient degree of intensity. The aquatic 

 Reptilia do the same in the dry season of hot countries. 



All living Reptilia belong to one of four orders. The majority are inhabitants 

 of the warmer parts of the world. 



I. Chelonia (Turtles and Tortoises). Body compressed in shape; the jaws 

 covered by a thickened epidermis and devoid of teeth; dermal skeleton well 

 developed ; its dorsal portion or carapace uniting with the neural spines and ribs of 

 the dorsal vertebrae, which are therefore immoveably fixed ; its ventral or plastron 

 covering the abdomen more or less completely. Head, neck, tail, and limbs often 

 retractile within the protection of the dermal skeleton. A urinary bladder and solid 

 grooved copulatory organ present. Marine, freshwater, and terrestrial ; occur in 

 fossil state from the Kimmeridge Clay onwards. 



II. Lacertilia (Lizards, Blindworm, &c.). Body covered by scales ; as a rule 

 two pairs of limbs, but one or other, or sometimes both pairs lost ; eyelids moveable, 

 rarely soldered and transparent; tympanic cavity seldom absent; jaws united 

 firmly at symphysis; shoulder-girdle present when fore-limb is aborted; cloacal 

 aperture transverse ; a urinary bladder and double copulatory organ. Terrestrial ; 

 one marine form, Oreocephalus (Ambfyrhynchus) cristatus, from the Galapagos Islands. 

 Iguana and Lacerta have been found fossil in Tertiary European strata. There are 

 several fossil groups; see Huxley, Anatomy of Vertebrated Animals, 1871. 



III. Ophidia. Body covered with scales ; in the majority a special series of 

 ventral ambulatory scales. Fore-limb, with shoulder-girdle always absent; hind- 

 limb and pelvis represented in a few. Body elongated; symphysis menti liga- 

 mentous and extensible ; eyelids transparent and always united ; no tympanic 

 cavity ; a transverse cloacal aperture and double copulatory organ. Terrestrial, 

 freshwater, or marine ; fossil only in Tertiary strata (London Clay, &c.). 



IV. Crocodilia. Body covered by scales and partially by scutes ; a long swim- 

 ming tail ; teeth implanted in sockets in the praemaxillae, maxillae, and dentary 

 bones; longitudinal cloacal aperture and solid grooved copulatory organ. Fresh- 

 water. The largest living Reptilia. The Gavials are found in the Ganges, and the 

 rivers of Borneo and N. Australia ; the Crocodiles in Africa, India, and as far east 



1 Martin-Saint- Ange states (p. 89, Etudes de 1'Appareil reproducteur, Paris, 1854) tnat Geoflroy 

 St. Hilaire and Florent Prevost succeeded in making the Common Grass Snake viviparous by 

 depriving it of water and maintaining a suitable surrounding temperature. On the Incubation of 

 the Python, see Forbes, P. Z. S. 1881. 



