PHYSIOLOGY OF THE INVERTEBRATA. 43 



(6) The Palceodidyoptera are found only in the fossil 

 condition. 



(7) The Bhynchota form an order of the Insecta having a 

 suctorial mouth in the form of a jointed rostrum. The order 

 includes the bugs (land and water), Aphides, Cicada, &c. 

 They all suck the juice of plants or the blood of animals. 

 According to Huxley, " there is a usually sharp and pointed 

 labrum, while the mandibles and maxilla are mere tubercles, 

 surmounted by long chitinous pointed styles, of which there 

 are four. The labium is usually represented by a median, 

 jointed, fleshy, elongated body, the anterior face of which 

 presents a longitudinal groove in which the mandibles and 

 maxillas are enclosed. Neither the maxillae nor the labium 

 are provided with palps." With such an arrangement of 

 parts one can readily understand the suctorial power of the 

 Ehynchota ; for it may be mentioned that the Cicadce perforate 

 the bark of the trees on which they live, and exhaust their sap. 

 The structure of these mandibles, maxillae, &c., are also well 

 adapted for piercing the skin and sucking the blood of animals. 



The Bhynchota have a crop, either forming an appendage 

 to the oesophagus, or forming an anterior dilatation to the 

 so-called chylific ventriculus, which in the Cicadce is of great 

 length. 



(8) The Diptera. — This order includes the fleas, flies, gnats, 

 crane-flies, &c. The mouth is suctorial, and is therefore 

 constructed on a somewhat similar plan to the last-mentioned 

 order ; but the maxillae have palps. In the house-fly " the 

 labrum, mandibles, and maxillae coalesce at their origins to 

 constitute the base of the probocsis, which is mainly formed 

 by the confluent second maxillae." 



The mouth leads into a narrow oesophagus which passes into 

 a crop situated upon the stomach. This is followed by a small 

 intestine which is convoluted, and then a short rectum provided 

 with two lateral glandular bodies — the so-called rectal glands. 



(9) The Lepidoptera. — In this order " the labrum and the 

 mandibles abort, and the labium is represented only by a 



