TORTOISES 249 



D. Senses. 



At the least noise the animal withdraws the unprotected parts of its 

 body into its shell, or, if it has its head above the surface of the water, 

 immediately disappears ; this indicates a sharp sense of hearing. The 

 tympanic membrane is exposed. The eyes are furnished with two lids 

 and a nictitating membrane. 



E. Food. 



The tortoise obtains its food in the water, and mostly at night-time. 

 It consists of worms, insects, frogs, newts and their larvae, and especially 

 fish. 



1. Hence it has its habitat in standing or slowly-running waters 

 (whence name pond tortoise). Its home is in Southern and Eastern 

 Europe. In Germany it is found in the basin of the Oder and Vistula, 

 as well as in the Havel and Spree. 



2. On land the tortoise progresses slowly and lazily on its short legs, 

 the whole of the soles of the feet being in contact with the ground. Its 

 heavy armour renders the body immovable, and hence incapable of assist- 

 ing in the animal's progress. (Compare, on the other hand, the other 

 reptilian orders. Notice how the tortoise turns over when it is placed 

 on its back.) In the water, however, the animal is very nimble. (Why 

 is this necessary ?) Its flat body, which recalls the form of a water -beetle 

 (contrast with land tortoises) cuts with ease through the water, and its 

 short legs, the toes of which are freely movable and united by webs, form 

 excellent oars (compare with other aquatic animals). 



3. Teeth are absent, their place being supplied by sharp-edged, horny 

 sheaths covering the jaws (compare with birds). By means of these, the 

 edges of the upper jaw overlapping those of the lower, the toothless 

 mouth can bite pieces out of its prey. Prey of large size (frogs, fish) is 

 held, while being consumed, by the strong nails of the toes. While a 

 tortoise is consuming a fish, the swimming-bladder of the latter fre- 

 quently rises to the surface of the water ; hence floating swimming- 

 bladders are always a sign of the presence of tortoises. 



F. Respiration. 



On account of the solid armour, breathing cannot be effected by 

 expansion and contraction of the chest. The animal, in fact, breathes 

 by closing its mouth and nostrils, and then forcing into the lungs — or, 

 as it were, swallowing— the air which has previously entered by the oral 

 and nasal apertures. (These swallowing movements may be distinctly 

 observed by watching the animal.) The nostrils are two dot-like 'aper- 



