THE LIZARD 355 



higher vertebrates. The testes and ovaries he dorsal, near the 

 kidneys, and discharge their products by special tubes (not 

 through the excretory tubules) into the cloaca. The eggs are 

 provided with a hard egg-shell and, in most pond and river 

 species, are laid in the spring in sandy soil at a depth of 30 to 

 80 centimetres. 



The muscular system of turtles is (in correspondence with 

 the round, bone-encased body) much reduced, except in the 

 neck and appendages, which are capable of varied and extraor- 

 dinarily rapid movements. 



The nervous system shows, at least so far as the brain goes, 

 a decided advance over amphibians. The lobes of smell are 

 reduced in size, and the cerebral hemispheres are well devel- 

 oped (Fig. 333). Also the cerebellum attains a fair size, inch- 

 eating increasing power of correlated movements. 



The sense-organs are well developed. Turtles are very 

 sensitive to touch, even on the sheU. They discriminate 

 between various sorts of closely related plants, showing a well- 

 developed sense of taste and smell. The ear shows no great 

 advance over that of Amphibia. The eye is protected by a 

 ring of bony plates in the sclerotic coat. In addition to two 

 eyelids there is a membrane — the nictating membrane — that 

 can be rapidly drawn across the front of the eyeball ; this we 

 shall see also in birds. It probably serves to cleanse the 

 front of the eye and perhaps to regulate the amount of 

 light entering the eye. Although not present in turtles, men- 

 tion must be here made of a third eye looking out from the 

 middle of the skull, and called the pineal ej^e. This eye is 

 functional in some lizards (Fig. 334). In our own brains there 

 is a rudimentary organ having the same relative position, and 

 which has long been known as the pineal gland. This organ 



