THE ORGANS OF DIGESTION. 157 



heart, their apex being attached to the last abdominal segment and the 

 colon, which has not yet been observed in other insects *. 



120. 



The anterior portion of the dorsal vessel which passes through the 

 thorax to the head, and which is not furnished with apertures and 

 muscles (PI. XXII. f. 8. c), may be called the aorta if we call the pos- 

 terior portion the heart. The part which may be considered as such 

 commences where the dorsal vessel bends near the thorax to pass into 

 its cavity, for from here the apertures and muscles are wanting. This 

 bend is greater or smaller, according to the size of the posterior par- 

 tition of the thorax, largest doubtlessly in the petiolated Hymenoptera 

 or the Diptera, whose thoracic cavity is entirely separated from the 

 abdominal cavity by the metaphragma. When the aorta arrives in the 

 cavity of the thorax its course becomes then direct as far as the head, 

 constantly keeping the central line, and accompanying the here straight 

 oesophagus or stomach, and frequently united to it by a cellular mem- 

 brane or the fatty substance. \Yhen there is a free and moveable pro- 

 thorax it passes likewise into this through the common opening, or more 

 rarely (as in Gryllotalpa f) through a small aperture in the meso- 

 phragma (PI. XI. No. I. f. 7- a], and here still accompanies the oeso- 

 phagus as far as the head. Here, close to where the oesophagus bends 

 down to the mouth, consequently behind the cerebrum, the aorta sud- 

 denly ceases with a somewhat distended orifice, without previously 

 sending forth any smaller vessel ; in other instances it divides in a fork, 

 each branch of which bends laterally, and terminates after a very short 

 course likewise with a free orifice; or, lastly, we find three short, equal, 

 radiating branches, each open at the extremity (for example, in Gri/l- 

 lus hieroglyphicus, Klug. J). 



121. 



We thus conclude the description of the blood-vessels of insects. 

 The most laborious and patient endeavours of Entomotomists to discover 

 other vessels remained unrewarded, until Joh. Miiller discovered a union 

 of the ovaries with the aorta . We shall treat in greater detail of this 



* Cornp. J. Miiller, iiber das Ruckengefass, in Nova Acta. Med. Nat. Car. vol. xii. pars 

 ii. pp. 576 and 586. 



f Ibid. p. 596. * Joh. Miiller, ib. p. 613. Ib. p. 613. 



