INTRODUCTION. XIX 



cally, and their office appears to be to prevent the 

 egress of the food. 



The mouth of those insects which suck is elon- 

 gated into a beak or tongue, or proboscis. 



This is a tube attached to the head of the insect. 

 In some, the bee for instance, it is composed of two 

 pieces connected by a joint, for if it were constantly 

 extended, it would be too much exposed to acci- 

 dental injuries : therefore, in its indolent state, it 

 is doubled up by means of the joint ; and in that 

 position lies secure under a scaly pent-house. In 

 many species of the butterfly, the proboscis, when 

 not in use, is coiled up like a watch spring. In 

 some insects, the proboscis, or tongue, or trunk, is 

 shut up in a sharp-pointed sheath ; which sheath 

 being of a much firmer texture than the proboscis 

 itself t as well as sharpened at the point, pierces the 

 substance which contains the food, and then opens 

 within the wound to allow the enclosed tube, through 

 which the juice is extracted, to perform its office. 



Antenna. — Almost all insects have two of these 

 organs. Their functions are not distinctly known : 

 in some insects they are organs of sense, in others 

 they exist, but are so- imperfect as to raise doubts as 

 to their utility ; nature, however, often repeats the 

 shape of a part without repeating its function ; 

 thus the mammae are allotted to males as well as 

 females : hence the non-existence of the function 

 in some animals cannot be taken as a positive 

 ground for denying the existence of that function 

 in similar organs in other animals. 



