THE FRESHWATER AQUARIUM 41 



in form, (6) altered in function ; lastly, (7) new parts may 

 be added. Thus (i) the middle finger is enlarged in the 

 horse ; (2) the side-toes are diminished in the pig ; (3) all 

 the toes but one are suppressed in the horse ; (4) the 

 radius and ulna are fused together in most hoofed animals ; 

 (5) the phalanges of a bat's fingers are altered in form, 

 becoming very long and slender ; (6) the hand of man 

 has changed its function, and has ceased to be an organ 

 of locomotion ; (7) the paddle of the whale contains many 

 additional phalanges. 



To everybody except anatomists the hand is an organ 

 for grasping, and when the thumb ceases to be opposable, 

 most of us would say that there is no longer a proper 

 hand. In the same way everybody except anatomists, 

 when the great toe as well as the thumb becomes oppos- 

 able, as in the gorilla or orang, would say that the animal 

 has got four hands instead of two. If there is no hand, 

 the functions of a hand may be performed by other parts. 

 Thus there are animals which grasp with the mouth (dogs, 

 birds), with the tongue (giraffe), with a proboscis, formed 

 of the enormously prolonged nose and upper lip (elephant), 

 or with the tail (spider- monkey). I could even tell you 

 of a fish (the sucking-fish), which holds on to floating 

 objects by the top of its head and neck. There are 

 animals which scratch or comb themselves with their 

 teeth, with the claws of the hind limb (birds), or with 

 spines on the tongue (lion, cat). While the same function 

 may be discharged by different parts, the same part may 

 discharge different functions. Thus the extremity of the 

 fore limb may be used as a hand, or as a paddle (whale), 

 or as a wing (bird), or as a fin (fish), or as a sucker (lump- 

 fish) ; lastly it may disappear altogether (serpent). 



IX. THE FRESHWATER AQUARIUM. 



The bell- jar and other small forms of aquarium are not 

 to be despised ; they serve to keep many aquatic animals 

 and plants alive for a short time, and suffice permanently 



