THE GENERAL ANIMAL FUNCTIONS 



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and nose is especially favorable. The senses thus far enumerated seem among 

 the earliest developed in the animal kingdom. 



in. Hearing and Equilibrium Sense. It is by no means certain that the lowei 

 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 (Culex pipiens). By J. W. Folsom. 



Questions on the figure. Compare with the antennae of a female (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 (Fig. 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 cells. 

 Late researches tend to prove 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 the general condi- 

 tions both of origin and structure appear to be much as described for the statocysts. 

 That is to say, the final sensory cells are ectodermal in origin, but now line a sac 

 deeply imbedded in the tissues of the skull. In some of the lower animals, as insects, 

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