INTRODUCTION. 



13 



reference to the jointed bodies in opposition to the bony articula- 

 tions of the Vertebrata. 



Again, regarding the little animals, the " Pets " of these 

 pages they formerly belonged to the class Reptilia, of which 

 Batrachia, Sauria, Ophidia, Chelonia, were four orders. But 

 now, as already explained, Batrachia is a class by itself, of 

 which Frogs and Newts are two orders, Anoura (without tails) 

 and Vrodela (with long tails), or, as our latest authority, Boulenger, 

 distinguishes them, Ecaudata and Caudata. 



And it is quite possible that renewed studies of the Reptilia 

 may lead to still farther divisions of Groups ; because, since the 

 publication of any of the works above quoted, a very remarkable 

 discovery has been made in some members of the lizard tribe — 

 no less than the existence of a third eye near the top of the head, 

 and directed skywards. Anguis fragilis, our English slow-worm, 

 is one of the lizards in which vestiges of this surprising organ 

 have been detected, and which will be further described in its 

 place. 



And this discovery is said to have been brought about through 

 the study of some small marine creatures which have not even a 

 head ! They are Acephalous molluscs, commonly known as " sea- 

 squirts," but scientifically Tunicates, or Ascidians, the former word 

 implying a tunic-like covering, and the latter their form, which is 



Fig 1. (Half natural size) a, incurrent 

 aperture; b, excurrent aperture. 



Fig 2. 



something like a leather sac or bottle (fig. 1). Just now I spoke 

 of the microscope revealing new organisms and unexpected relation- 



