474 



CHORDATA. 



branches ending in tactile discs. Though long known among terrestrial 

 vertebrates, these have recently lieen found in fishes. 



The (iiih-shapeJ corpuscles (also known as ]\ilci--ri.ic!iiiaii corpuscles, 

 iig. Si) are allied to the tactile corpuscles liy form and mesodermal 

 position, although thev diiTer materially in structure and are not easily 

 to be regarded as ectodermal in origin, since they occur not only in the 

 skin but in deeper structures like the mesentery of the cat. The latter 

 position rentiers their function proldematical. 



\Miile in the terrestrial vertebrates typical scnsor\- epithelium is lack- 

 ing, it attains a high development in the skin of fishes. The dermal 

 nerves pass into the epidermis and end in o\al corpuscles, which, while 

 imbedded in a stratihed epithelium, consist of a single layer of sense and 

 supporting cells. According to structure, ;/<•/-:'(• hillocks (nciiromasts) and 

 tiervc-ciid buds are distinguished. The lirst are the specihc organs of the 



Fig. 52q. 



Fig. 



Fig. 520. — Section of olfactory cpilliclium of a lisli Bdoiic (from O. Ilcrtwig, after 

 Blaue). c, epitlielium: k, olfactory buds; ;;, ner\-es. 



Fig. c;:;o. — Diagram of nose of lizard (after \\'iedersheimV .1 -V, outer nasal 

 cavity. C oIfactor\* sac: Cii, Stcnson's duct; Ch. choana; /A', inner nasal ca\"it\-; MS, 

 roof of mouth; P, Jacobson's organ; f, connc.\ioii between nasal cavities. 



lateral line, to be mentioned later, of tlshes and branchiate amphibians 

 and amphibian larv;e, and therefore appear to subserve special and im- 

 portant sensations connected with aquatic life. The end buds are 

 especially collected in the neighborhood of the mouth, on the lips and l.>ar- 

 bcls. Since they also occur in the mucous membrane of the mouth, 

 especially in the palatal regions, they connect with the taste organs. The 

 taste Inids have the same structure as the end l)uds of tishes. Thev occur 

 in all classes of vertel)rates, and are most abundant in man in the walls of 

 the circumvallate papilla? at the l.)ase of the tongue; in rodents on the large 

 foliate papilLe, etc. 



Wliether the end buds are related to the olfactory organs is questionable. 



