330 CHELONIA CHAP. 



The SENSE OF HEARING is apparently not very acute, although 

 tortoises and turtles are frightened by noise, and can distinguish 

 sounds ; otherwise they would have no voice, which is very tiny 

 and piping in most tortoises during the pairing season. In most 

 water-tortoises the tympanic membrane is thin and quite exposed ; 

 in land-tortoises it is often thick and covered by the ordinary skin ; 

 lastly, in Chelone the tympanic cavity is filled with a plug of 

 the much-thickened skin, possibly in adaptation to the water- 

 pressure when these creatures dive to considerable depths. The 

 ossicular chain is mostly reduced to a long, bony, columellar rod. 



The SENSE OF SMELL is well developed. All Chelonians care- 

 fully smell their food, in the air as well as under water. The 

 individual predilection shown by many species for different kinds 

 of animal and vegetable food, since they are, for instance, able 

 to distinguish between the various sorts of cabbage, cauliflower, 

 sprouts, etc., proves that they possess a considerable amount of 

 smell and taste. 



Tortoises have a fine sense of touch ; even the slightest tap 

 on the shell is noticed, and the skin of the soft parts is extremely 

 sensitive. Tickling of the sides of the tail, or of the hinder 

 surface of a thigh, produces ridiculous scratching actions of the 

 same or of the opposite foot. 



The digestive apparatus is simple. Only a few peculiarities 

 need be mentioned. The tongue is mostly broad and soft ; it 

 cannot be protruded. The oesophagus of the Chelonidae is covered 

 with many conical projections pointing towards the stomach. The 

 latter is simple, except in Sphargis. The intestine is devoid of a 

 caecum, but the difference between the small intestine and the 

 rectum is very marked and often abrupt. The cloaca is very 

 roomy. It contains the large copulatory organ, which is unpaired, 

 grooved on its dorsal side, and is altogether constructed like that 

 of the Crocodilia. The large bladder opens ventrally into the 

 urodaeum, a recess of the cloaca ; near its base open the urinary 

 and genital ducts. Many water-tortoises possess also a pair of 

 lateral thin -walled sacs, the so-called anal sacs, dorso- lateral 

 diverticula of the walls of the urodaeurn. These sacs, which 

 have highly vascularised walls, are incessantly filled and emptied 

 with water through the vent, and act as important respiratory 

 organs. When such a water-tortoise, for instance an Emys or a 

 Clemmys, is suddenly taken out of the water, it squirts out a 



