30 NERVOUS SYSTEM AND SENSE-ORGANS 
in-pushing from the exterior the cells in question are of ecto- 
dermic nature. The largest amount of specialization takes place 
in Mammals, where the “taste-buds”, as the group of cells are 
called, are associated with small projections or papilla of the 
surface of the tongue (fig. 1036). 
SMELL 
Many of the lower animals can undoubtedly smel: as well 
as taste, though to definitely associate this sense with special 
cells or groups of cells is not at present possible. Our know- 
ledge is more complete in the case of Arthropods, Molluscs, 
and Vertebrates, where experiments lead to results of more de- 
groups of olfactory setze on its under side, enlarged; 4, an olfactory seta, further enlarged. , Tip of feeler of a Milli- 
pede, greatly enlarged, showing olfactory cylinders among the ordinary tactile bristles. cv, Two olfactory cones from 
feeler of a Wasp, in section, greatly enlarged. 
finite kind. In all cases the stimulus is of a gaseous nature, 
and in aquatic animals the gases that are smelt are dissolved 
in the surrounding water. The sense of smell is obviously of 
great importance as regards adjustment to the environment. By 
its means food is in many cases detected, while it often enables 
animals to recognize friends or foes, even when these are at a 
considerable distance. This is, of course, due to the nature of 
the stimulus. Since Smell, Hearing, Sight, and the Temperature 
Sense are able to give information about objects which are more 
or less far away, they may be grouped together as Distance-Senses 
(teleesthetic senses), and are in marked contrast to Touch (so far 
as haptic sensations are concerned), which only conveys knowledge 
regarding things that actually come into contact with the skin. 
