LIFE IN SECONDARY TIMES 279 



of the Secondary Period could only move their huge bodies 

 with some difficulty. Moreover, in the higher organisms, the 

 body-heat is preserved by the layer of air which feathers or 

 fur keep at a constant temperature. A shorn rabbit soon dies. 

 The large Reptiles of the Secondary Period had no such pro- 

 tection, and the heat produced in their bodies by respiratory 

 processes would be dissipated, not only by the surface of the 

 trunk, but also by the long neck and enormous tail. So long 

 as the external temperature remained warm and fairly constant 

 they did not suffer from these imperfections, and the Birds and 

 Mammals had no advantage over them. It was otherwise when 

 extremes in temperature became greater. Their lives would 

 be punctuated by more or less lengthy periods of torpor, 

 during which they would be at the mercy of animals having 

 a constant body temperature, such as Mammals and Birds, 

 which could maintain the same activity at all times. Thus the 

 Reptiles became an easy prey. Indeed, it was inevitable that 

 they should disappear before the increasing number of their 

 rivals. The composition of present day reptilian fauna 

 furnishes a powerful argument in favour of this explanation. 

 The flower of the reptilian class has disappeared ; none but 

 a few species of Crocodiles have survived — species that hide in 

 water and are further protected by solid armour ; or Chelonians 

 that, enclosed in a carapace, are almost impossible to extract ; 

 together with Lizards set low on their legs, and Snakes with 

 none at all, which are therefore able to hide themselves in holes 

 and the interstices of rocks inaccessible to the majority of 

 preying animals ; or those endowed with special means of pro- 

 tection, such as the green colour of Dendrophis, the Tree-snake, 

 the faculty the Chameleon possesses for changing its colour, 

 or weapons as treacherous as they are formidable, such as the 

 venom of Helodermes among Lizards, and, above all, the 

 poison of snakes. All those Reptiles which were not able to 

 dissimulate their presence or to defend themselves by treachery, 

 have disappeared : the existing class consists only of those 

 which escaped in the struggle for existence. 



Apart from a few Scincoid Lizards such as the Slow-worm, 

 and several Snakes like Vipers and the marine Snake or 

 Hydrophis, the Reptiles of the present epoch lay eggs. The 

 Ichthyosaurians, and perhaps Compsognathus, were viviparous, 

 but there is no evidence that this method of reproduction, 



