XX INTRODUCTION. 



proventriculus, which is always present, by a distinct constriction, ami 

 having the Avhole or greater part of the upper surface covered with long, 

 thin flocks, which originate from the inner nincous membrane of the 

 stomach, and are evidently secreting organs, whose secretion makes more 

 soluble the heavily digestible animal matter (v. Burmeister, 1. c. p. 132). 

 The divisions of the intestinal canal which follow the stomach are usually 

 simple, and do not present many changes of form, although they vary 

 considerably in length. 



The nervous system is formed of a series of ganglia or nervous centres 

 united by one or two cords of nerve ; these ganglia difler in number, but 

 as a general rule "the ventral cord has .as many ganglia as there are 

 freely movable divisions of the body :" the larvte of the Lepidoptera 

 and carnivorous Coleoptera possess as many ganglia as segments ; in the 

 Diptera in which the three segments of the thorax are united and agglu- 

 tinate we find only one thoracic ganglion, and further in those larvae in 

 Avliich tlie bodies are thick and fat and possess no distinct segments 

 (e.g. iu the Lamellicornia) there is no distinct ganglion, but a simple 

 cord from which the nerves pass off on each side ; in the perfect beetle 

 there are less ganglia than in the larva, and there are less in species 

 belonging to some families than in those belonging to others. 



The circulatory system consists of a heart, or an organ answering to a 

 h(!art, divided into several chambers arranged longitudinall}', and opening- 

 one into the other, by means of the alternate contraction and dilatation 

 of which a white cold clear fluid corresponding to blood is circulated 

 through the so-called blood-vessels, which appear to be closely connected 

 Avith. the trachete of the respirati ry system. 



The respiratory system is made up of the external spiracles or stiyniata, 

 and the internal tracliece : the former are apertures on the surface of the 

 body by means of which air is taken in, and the latter are the tubes by 

 which it is distributed throughout the system ; there are two large con- 

 necting trachete from which smaller branches ramify ,in every direction 

 over the body : in the Coleoptera we may say, roughly speaking, that 

 each segment of the body has a spiracle, or perhaps more correctly that 

 one is to be found on the boundaries of every two segments ; their shape 

 and position in some families, e.g. the Dytiscidte, afford good characters for 

 the distinction of genera. Gills or branch ke are very rarely found in the 

 Coleoptera ; they occur, however, in certain larvae (e.g. Gyrlnus, Cnemi- 

 dotus, Hydrous carahoides, Berosus, &c.) in the form of processes, fringed 

 or otherwise, arising from the sides of the segments : all those insects 

 which are not provided with gills have to rise frequently to the surface 

 of the Avater to obtain the requisite supply of air which they in most 

 cases draw more especially through the spiracles situated at the posterior 

 end of the body. 



TJie organs of generation are variously modified, and consist of a male 

 intromittent organ and a female receptacular organ and ovipositor ; the 

 sexes are always separate : in some groups a most important specific 

 character is afforded by the cedeagus, whicli some writers most erroneously 



