SON- VOCAL LANGUAGE. 311 



5. Emission of smells or odours, mostly pungent and 

 disagreeable. 



6. Emission of light, including so-called ' phospho- 

 rescence.' 



E.g. in the glowworm. 



7. Physiognomy facial expression, the play of feature, 

 peculiarities of countenance including especially the look, 

 stare, or gaze of the eye, constituting what has been called 

 eye language ; and also including 



a. Grimace. 



E.g. in apes and baboons. 



b. Vacancy of feature, usually indicative of disease. 

 Of all the non-vocal forms of animal language the most 



important to the student of comparative psychology is pro- 

 bably the last. But there are great difficulties in the study 

 of feature-changes in the lower animals, and in their com- 

 parison with those occurring in man, the principal being the 

 fact that the face in other animals is so frequently covered 

 with hair, feathers, or other cutaneous adjuncts or ap- 

 pendages, that prevent our seeing the play of the facial 

 muscles. The physiognomy of the lower animals can, there- 

 fore, be best or only studied in those that are bare-faced, 

 the number of whom is extremely limited. There are, how- 

 ever, a few literally or comparatively bare-faced monkeys, 

 apes, or baboons such as the mandrill dogs, and other 

 animals, in which even the phenomenon of blushing, or 

 flushing of the skin, and its converse can be observed. 



Two points are especially noteworthy in our consideration 

 of facial expression in the lower animals 



1. Its eloquence the number of mental states of which it 

 is the correlative and 



2. Its wonderful variety or variability, not only in different 

 genera and species, or in different individuals of the same 

 species, but even in the same individual at different times 

 or under different circumstances. 



In the dog and horse especially the whole phenomena of 

 feature-change of the varying states of the countenance 

 in particular of the look and eye as the signs of feeling, 

 may be studied with equal advantage and interest. The 



