ORGANS OF THE SENSES. 2/7 



vations of Camparetti on that of the scarabseus and several 

 other genera of insects. At the lower and lateral part of the 

 head there is a minute round passage closed externally by 

 a membrane, and leading on each side of the head to an 

 internal vestibular sac, with two small curved canals ex- 

 tending from it. These vestibular cavities are furnished 



O 



with distinct nervous filaments, which appear to be branches 

 of the antenneal nerves, and they constitute an acoustic 

 organ which has been observed in many different forms of 

 this class. They are placed more anteriorly on the head of 

 the locusts, where the minute canals are thin, membranous, 

 and transparent, and this organ presents different degrees 

 of development in different species of locusts. Similar audi- 

 tory organs have been detected in the cicada, vespa, libelluke, 

 and at the sides of the base of the long spiral proboscis of 

 the papiliones ; they are perceived also in ants, flies, and 

 other insects belonging almost to every order of this great 

 class. This delicate organ contained entirely within the 

 cranial cavity of insects is provided with a vestibular opening 

 or fenestra ovalis covered with a thin and tense membrane 

 to receive the sonorous undulations of the air and to convey 

 them to the ento-lymph of these membranous cavities, and 

 so to the expanded surface of the surrounding delicate 

 auditory nerves. These organs have been also dissected and 

 described in many insects by Ramdohr, who observed them 

 in the common bee placed near the base of the maxillae. 

 Treviramus found those of the blatta orientalis placed behind 

 the basis of the antennae and closed by an oval, white, 

 concave, vestibular membrane, and Blainville found them 

 in the cicadae, which distinctly hear, on each side of the 

 back part of the head, in form of two minute open stigmata 

 leading to vestibular sacs, but many entomologists, as Straus 

 and Burmeister, are inclined to place the auditory organs of 

 insects in the antennae themselves. In the class of arachnida, 

 which also breathe and reside in air, organs of hearing very 

 similar to those of insects were detected by Camparetti in the 

 spiders, placed near to the mouth at the bases of the palpi 

 and consisting of a vestibular sac covered by a transparent 

 membrane, through which the auditory nerves could be per- 

 ceived. The density of texture and the deep hues of the 



