AND THE LOWER ANIMALS. 91 



extent, and more distinctly as regards the loco- 

 motive system than any other. We wish we could 

 give the reader the details of this subject just as 

 they have been given by A. Duges, but the cha- 

 racter of this work forbids our going beyond gene- 

 ralizations.* 



The tadpole at first exhibits no trace of either 

 internal or external limbs. It swims about like a 

 fish by the action of its tail,t which is an extensive 

 organ, longer and wider than the body, supported by 

 a prolongation of the vertebral column, moved by 

 powerful muscles, and supplied with large blood- 

 vessels and numerous nervous branches. Beneath 

 the skin and muscles of the anterior and posterior 

 regions of the body two little projections appear at a 

 certain period. These are the limbs, and are at first 

 attached to the adjacent structures by the nerves and 

 blood-vessels which are supplied to them. These pro- 

 jections increase in size, their appendages appear in 

 due course, and eventually the hip and shoulder bones 

 are developed. As soon as these locomotive organs 

 enter upon the discharge of their functions, the tail 

 begins to disappear. Its skin, muscles, nerves, bones, 

 and blood-vessels atrophy, and vanish from our sight. 



* * Eecherches sur l'Osteologie et la Myologie des Batrachiens a 

 leurs differentes ages," 1834. This work, which is from the pen of one 

 who was prematurely removed from among us, obtained the phy- 

 siological prize awarded by the Academie des Sciences. 



t Fishes' fins seem rather to guide them when swimming than 

 to aid directly in producing motion. At most they are employed 

 in the latter capacity when the movements are very slow, and are 

 also of use in stopping progression. It is the tail alone which urges 

 forward the fish with rapidity. We may easily be convinced of the 

 truth of this statement by watching the movements of gold-fish in 

 an aquarium. 



