REPTILES, AMPHIBIANS, FISHES, AND THE 

 LOWER VERTEBRATES 



BY J. ARTHUR THOMSON, M.A. 

 Professor of Natural History, University of Aberdeen 



CHAPTER XV 



STUDY OF REPTILES 



REPTILES are so few and far between in Britain that they cannot 

 bulk largely in school Nature Study. But, partly because they 

 are comparatively rare, they excite strong interest, and every 

 opportunity of studying them should be utilised. 



The diverse animals tortoises, lizards, snakes, crocodilians, 

 and Sphenodon which are classed together as Reptiles, are the 

 modern descendants of those vertebrates which first became 

 quite independent of the water, and began to follow the hint 

 given by their forerunners, the Amphibians, of possessing the 

 dry land. While almost all Amphibians spend at least their 

 youth in the water, breathing by gills, this is not necessary for 

 Reptiles, in which the newly hatched animal breathes by lungs, 

 and the unhatched embryo by having blood-vessels spread out 

 on a delicate birth-robe or foetal membrane (the allantois). As 

 in still higher vertebrates, gill-s/^s are present in the embryo, 

 remarkable reminiscences of aquatic ancestry, but they are 

 not used in respiration, and there is no trace of gills. 



Reptiles seem to form among vertebrates a great central 

 assemblage, like " worms " among invertebrates, more like a 

 number of classes than a single class, exhibiting close affinities 

 with Birds, somewhat less close with Mammals. The five orders 

 or subclasses which are represented to-day have been already 

 referred to, but it must be noticed that more than five orders, 



such as Ichthyosaurs, Plesiosaurs, and Deinosaurs, have long since 



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