82 ZOOLOGY 



and nose is especially favorable. While both smell and taste are aroused by chem- 

 ical stimuli, very much less of the substance is necessary to arouse smell than is 

 required for taste. Thus smell serves to make the organism aware of slight 

 changes in the medium and of distant objects, while taste is a sense of near-by 

 objects only. The senses thus far enumerated seem among the earliest developed 

 in the animal kingdom. 



III. Hearing and Equilibrium Sense. — It is by no means certain that the lowet 

 animals possess the ability to appreciate those vibrations in matter (air, water, 

 etc.), which arouse in us the sensation of sound. There are in several groups of 

 such animals organs, the structure of which would suggest that they might receive 

 vibrations of the medium in which they live. In their simplest condition they 

 consist of a sac [otocyst or statocyst) derived from the ectoderm and lined by an 

 epithelium containing sensory cells. From these cells sensory hairs extend into 



Fig. 42. 



Fig. 42. Antenna of Male Mosquito {Cutex pipiens). By J. W. Polsom. 



Questions on the figure. — Compare with the antennae of a fepjiale (see Fig. 65). 

 What are the differences between the head of the male and female mosquitoes? 

 What is believed to be the function of these plumose antennas? What are the 

 evidences for this view ? 



the cavity (Pig. 41). The cavity contains a fluid which may support one or more 

 solid particles {statoliths) . With the vibration of the medium the whole would be put 

 into vibration, but the inertia of the contained fluid and statoliths would cause the 

 latter to strike against the hairs and thus serve as stimuli to the sensory eels. 

 Late researches prove, however, that these structures are organs enabling the 

 organism to appreciate the pull of gravity and movements in the water rather 

 than to hear. In higher forms the ear becomes immensely more complex, but 



