CHAPTER VII 



THE NERVOUS SYSTEM AND THE SENSE ORGANS 



I. THE SENSE ORGANS. 



The sense organs are structurally suited to receive sen- 

 sory impressions from the outside world. They are all 

 connected with the brain. Two rather distinct types of 

 sense organs may be recognized, the much specialized sense 

 organs having many associated structures such as those 

 connected with sight and hearing, and the simpler integu- 

 mentary sense organs concerned with touch and perception 

 of temperature. Dissection of the brain often ruins the 

 ear and eye. Therefore, it is advisable to study the sense 

 organs first. 



1. Integumentary Sense Organs. 



A. Several integumentary sense organs are present in 

 the skate. The ampullae of Lorenzini occur in five groups 

 on the head. Remove a piece of skin from the ventral side 

 of the head. The pores lead into the canals of Lorenzini 

 which end in a very small bulb, the ampullae of Lorenzini 

 supplied with white nerve fibers. These organs seem to 

 function in the perception of vibrations and pressure 

 stimuli from the water. 



B. The lateral line system consists of several canals, 

 chief of which are: the supraorbital canal above the eye 

 extending forward at the side of the rostrum ; an infra- 

 orbital canal which separates from the supraorbital back 

 of the spiracle ; the lateral line canal extending backwards 



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