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TEXT-BOOK OF ENTOMOLOGY 



The aorta. - - While the heart is mostly situated within the 

 abdomen, it is continued into the thorax and the head as a simple, 

 non-pulsating tube, called the aorta. In Sphinx the aorta, as de- 

 scribed by Newport, begins at the anterior part of the 1st abdominal 

 segment, where it bends downwards to pass under the metaphragma 

 and enter the thorax; it then ascends again between the great 

 longitudinal dorsal muscles of the wings, and passes onwards until 

 it arrives at the posterior margin of the pronotum ; it then, again 

 descends and continues its course along the upper surface of the 

 ossophagus, with which it passes beneath the brain, in front of which 

 and immediately above the pharynx, it divides into two branches, 

 each of which subdivides. Newport, however, overlooked a thoracic 

 enlargement of the aorta called by Burgess the " aortal chamber" 

 (Fig. 310, a, c). 



" In Sphinx and Vanessa urticce, immediately after the aorta has passed 

 beneath the cerebrum, it gives off laterally two large trunks, which are each 

 equal in capacity to about one-third of the main vessel. These pass one on 

 each side of the head, and are divided into three branches which are directed 

 backwards, but have not been traced farther in consequence of their extreme 

 delicacy. Anterior to these trunks are two smaller ones which appear to be 

 given to the parts of the mouth and antennae, and nearer the median line are 

 two others which are the continuations of the aorta. These pass upwards, and 

 are lost in the integument. The whole of these parts are so exceedingly 

 delicate that we have not, as yet, been able to follow them beyond their origin 

 at the termination of the aorta, but believe them to be continuous, with very 

 delicate, circulatory passages along the course of the tracheal vessels. It is in 

 the head alone that the aorta is divided into branches, since, throughout its 



whole course from the abdomen, it is one 

 continuous vessel, neither giving off branches, 

 nor possessing lateral muscles, auricular ori- 

 fices, or separate chambers." (Newport, art. 

 Insecta, p. 978.) 



O 



-b 



FIG. 373. A, last three abdominal 

 segments and bases of the three caudal 

 processes of I'lofmi <l ijitvrititt : r, dor- 

 sal vessel; k'l, ostia; /, >peeial terminal 

 chamber of the dorsal vessel with its 

 entrance </ ; />, blood-vessel of the left 

 caudal process. I{. W\\\\ joint of the left 

 caudal appendage from In-low : /, a por- 

 tion of the bliMxI-vessrl ; ft, orifice in the 

 latter. After Zimmerman!), from Sharp. 



Dogiel observed in the transparent 

 larva of Corethm plumicornis that the 

 aorta extends only to the hinder border 

 of the brain. Here it divides into two 

 lamellae, each of which independently 

 extends farther on. One lamella is 

 seen under the brain and under the 

 eye, the other reaches near the eye. 

 The lamellae are tied to the integument 

 by threads. At the point of division of 

 the aorta is an opening. (Kolbe.) 



True blood-vessels appear to exist in the caudal appendages of the May-flies, 

 as the heart appears to divide and pass directly into them (Fig. 378). The last 



