CIRCULATION OF BLOOD IN INSECTS. 671 



teeth of the opposite side. Each half, moreover, may be ascer- 

 tained to contain a Trachea or air-tube (§ 524) ; and it is probable, 

 from the observations of Mr. Newport, * that the sucking-up of the 

 juices of a flower through the Haustellium (which is accomplished 

 with great rapidity) is effected by the agency of the Respiratory 

 apparatus. The Proboscis of many Butterflies is furnished, for 

 some distance from its extremity, with a double row of small pro- 

 jecting barrel-shaped bodies (shown in Fig. 345), which are sur- 

 mised by Mr. Newport (whose opinion is confirmed by the kindred 

 inquiries of Dr. Hicks, § 518) to be organs of Taste. — Numerous 

 other modifications of the structure of the Mouth, existing in the 

 different tribes of Insects, are well worthy of the careful study of 

 the Microscopist ; but as detailed descriptions of most of these 

 will be found in every Systematic Treatise on Entomology, the fore- 

 going general account of the principal types must suffice. 



521. Parts of the Body. — The conformation of the several 

 divisions of the Alimentary Canal presents such a multitude of 

 diversities, not only in different tribes of Insects, but in different 

 states of the same individual, that it would be utterly vain to 

 attempt here to give even a general idea of it ; more especially 

 as it is a subject of far less interest to the ordinary Microscopist 

 than it is to the professed Anatomist. Hence we shall only stop 

 to mention that the "muscular Gizzard in which the (Esophagus 

 very commonly terminates, is often lined by several rows of strong 

 Horny Teeth for the reduction of the food, which furnish very 

 beautiful Microscopic objects, especially for the Binocular. These 

 are particularly developed among the Grasshoppers, Crickets, and 

 Locusts, the nature of whose food causes them to require powerful 

 instruments for its reduction. 



522. The Circulation of Blood may be distinctly watched in 

 many of the more transparent Larvae, and may sometimes be observed 

 in the perfect Insect. It is kept-up, not by an ordinary heart, but 

 by a ' Dorsal Vessel ' (so named from the position it always occupies 

 along the middle of the back), which really consist of a succession 

 of Muscular Hearts or contractile cavities, one for each Segment, 

 opening one into another from behind forwards, so as to form a con- 

 tinuous trunk divided by valvular partitions. In many Larva?, 

 however, these partitions are very indistinct, and the walls of the 

 ' Dorsal vessel ' are so thin and transparent that it can with diffi- 

 culty be made-out, a limitation of the light by the Diaphragm 

 being often necessary. The blood which moves through this trunk, 

 and which is distributed by it to the body, is a transparent and 

 nearly-colourless fluid, carrying with it a number of ' oat-shaped ' 

 corpuscles, by the motion of which its flow can be followed. The 

 current enters the Dorsal Vessel at its posterior extremity, and is 

 propelled forwards by the contractions of the successive chambers, 

 being prevented from moving in the opposite direction by the valves 



* "Cyclopaedia of Anatomy and Physiology," Vol. ii., p. 902. 



