438 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



set upon papillae, and are most numerous on the cir- 

 cumvallate papillae at the back of the tongue ; in 

 rabbits and hares a large supply of taste bulbs is to be 

 found on an organ developed on either side of the 

 root of the tongue, which is broken up into ten to 

 fourteen valleys, in the recesses of which the bulbs are 



Fig. 187. A, Taste Bulbs of Babbit ; B, Transverse Section through 

 Taste Folds of Eabbit. ( Ai ter Engelmann. ) 



placed. In this sense, then, as in others, we find that 

 the terminal sense organs are withdrawn from the 

 surface, protected from rough contact, and excited 

 only by certain definite stimuli. This must not lead 

 us to suppose that the gustatory sense organs offer 

 any exception to the rule that all organs of sense have 

 their origin in the epiblast of the embryo. 



Olfactory organs. Till we reach the Arttiro- 

 poda and Ulollusca we do not find any structures 



