FRAGILITY OF THE TAIL IN LIZARDS 103 



Crocodiles, Lizards, and Snakes of North America, says 

 (p. 190): "In a good many families the caudal ver- 

 tebrae are divided by a transverse fissure or suture in 

 front of the middle, which often splits the base and 

 sometimes the length of the diapophysis. Such a 

 structure is seen in Iguanidae {Iguana, Saitromalus, 

 Sceloporus, Bipsosaurus), Anolidse, Anguidae (Celestus), 

 Teiidae (Tupinamhis, Gnemidophoriis), Lacertidae {La- 

 certa), and Scincidae {Gongylus, Eumeces). In Bipso- 

 saurus, Anolis, and Lacei^ta, the neural spines of the 

 vertebras (caudal) are double ; in the other genera 

 named, single. In Varanidce, Helodermidce, Gerroiiotus, 

 Crotaphytiis, and Plirynosoma, the caudal centra are un- 

 divided, and the neural spines are single. In Ophisaurus 

 the centra are undivided, and the neural spines double. 

 The centra are excessively thin in Ophisaurus, so that 

 they break more readily than they disarticulate." 



In Sceloporus, which is a common species in Mexico 

 and the Southern United States, this segmentation of 

 the centra of the caudal vertebrae is present only from 

 about the eighth vertebrae. Professor Packard in his 

 Text- Booh of Zoology (p. 502), says: "In many lizards 

 {Lacerta, Iguana, and the Geckos), the middle of each 

 caudal vertebra has a thin cartilaginous partition, and 

 it is at this point that the tails of these lizards break 

 off so easily when seized." 



In British text-books on Zoology, the anatomy of 

 the Eeptilia is usually very deficiently dealt with ; 

 but Dr. Hans Gadow's recently pubHshed work on 



