404 



CHORUATE ANATOMY 



three later disappear, leaving the maxillary and two ethmoid conchae 

 characteristic of the adult. 



TASTE ORGANS 



The second of the chemical senses is taste which, as we have seen, has 

 a common origin with smell. All animals respond in one way or another 

 to substances dissolved in water. Specialized taste organs in the form 

 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. 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 



SENSORY 

 (PELLS 



/SENSORr BRISTLE 



SENSORY BRISTLE 



EPIDERMIS \ 



NERVE FIBERS 



NERVE FIBERS 



A. ANNELID B. FISH C. MAN 



Fig. 356. — Diagrams of taste-buds in .4, annelid, B, fish, and C, man, showing 

 their fundamental similarity. (Redrawn after Fritz Kahn, " Der Mensch," Albert 

 Mviller, Zurich.) 



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 

 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 in higher 

 forms. (Fig. 356) 



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. 



