150 ANATOMY AND PHYSIOLOGY 





usually straightest in larvae, (particularly in cater- 

 pillars,) and in the imago it curves downwards 

 between the thorax and abdomen, to enable it to pass 

 through the narrow isthmus by which these parts 

 are united. On close examination it is found that 

 the coats of this vessel are composed of two mem- 

 branes, the exterior of which is dense and muscular. 

 Such at least appeared their composition to Strauss, 

 but Mr. Newport detected a third membrane of an 

 extremely thin and delicate texture. 



The greater portion of the vessel contained in the 

 abdomen, consists of a consecutive series of chambers 

 or cells, separated from each other either by single 

 or double valvules, which permit the transmission of 

 the blood from behind forwards, or in the direction 

 of the head, but prevent its retrograde motion, " A 

 little behind these valvules, on both sides of each 

 chamber, there is a transverse opening, likewise 

 having a semilunar valvule internally, which allows 

 the blood to enter the organ and opposes its exit. 

 The number of the cells varies according to the 

 species, or rather the families. M. Strauss found 

 eight in the Melolontha vulgaris, M. Burmeister five 

 in the larva of Calosoma Sycophanta, while M. J. 

 Miiller discovered only one in Phasma ; but in this he 

 was probably mistaken. However this may be, the 

 organization in question explains at once the pro- 

 gress of the blood in the dorsal vessel, and the reason 

 of it being always filled. For when the hinder cell, 

 which is usually shorter than the others, and which 

 we shall suppose full of blood, contracts, the fluid, 

 pressed on all sides by the containing vessel, is forced 



