578 



COMPARATIVE ANATOMY 



of taste-buds occur in annelids, in which they are scattered over the 

 surface of the body, but are more numerous in the mouth region; and 

 experiment demonstrates that leeches can taste. In molluscs, neurosen- 

 sory cells connected with subcutaneous ganglia surround the mouth. A 

 few insects have gustatory hairs or bristles on the antennae, and some 

 have them around the mouth. With the exception of the taste-buds, 

 none of the invertebrate sense organs appears to have a genetic relation 

 with those of chordates. 



The organs of taste of chordates are taste-buds, with a core of sensory 

 hair cells and an outer rampart of supporting cells. Unlike the cells of 

 the neuromasts, however, both sensory and supporting cells of taste-buds 

 are of equal length, and the sensory as well as the supporting cells rest 



SENSORY 

 tPELLS 



(SENSORY BRrSTLE 



SENSORY 

 SENSORY BRISTLE ^^'■'^ 



.SENSORY BRISTLE 



'rEPIOERMIS 



NERVE FIBERS 



A. ANNELID B. FISH C. MAN 



Fig. 477.— Diagrams of taste-buds in A, Annelid, B, Fish, and C, Man, showing 

 their fundamental similarity. (Redrawn after Kahn's "Das Leben Des Menschen," 

 W. Keller & Co.) 



upon the basement membrane of the epidermis. Each hair cell of a 

 taste-bud is a secondary sense cell, which is supplied by the dendritic 

 terminations of sensory nerves. Taste-buds differ little in lower and 

 higher vertebrates, though tending to be less widely distributed over the 

 bodies of higher forms. (Fig. 477) 



In amphioxus, clusters of hair-cells connected with sensory nerves 

 occur in the velum and the oral cirri. A chemical sense, whether smell 

 or taste would be difficult to say, may therefore be ascribed to this animal. 

 That similar sense organs are generally distributed over the surface of the 

 body has not been demonstrated. Consequently, if the arrangement of 

 taste-buds in amphioxus may be taken as primitive, the chordates start 

 their phylogenesis with a high degree of concentration in the distribution 

 of their organs of taste. 



Pharyngeal taste buds occur in larval cyclostomes, while in the aciult 

 they are present also on the surface of the head. In elasmobranchs the 

 taste-buds are limited to the lining of the mouth and pharynx, chiefly 

 on the surface of papillae. In ganoids and teleosts they are found on the 



