448 SANGUIFEROUS SYSTEM. 



cope, and the soft parts of perfect insects, newly escaped 

 from their larva covering, it was distinctly seen by several 

 accurate observers, as Leuwenhock, Nitzch, and Baker, that 

 there is a motion of blood, containing globules, in different 

 parts of the living body of these winged articulata. It was 

 especially observed by Baker, that in certain larvee a motion 

 of blood globules is obvious, extending forward along the 

 middle of the back, and returning backwards along the sides 

 of the body thus completing the circulation. The anterior 

 divisions of the dorsal vessel being concealed by the opacity 

 of the head, it was for some time supposed that that vessel 

 propelled its contents, by an open anterior orifice, into the 

 general cavity of the trunk, and that the fluid, by being re- 

 admitted into the posterior part of the dorsal vessel, thus 

 performed a circular motion. The sacculated structure of 

 the dorsal vessel, (Fig. 133. D. a. b,) or heart of insects, had 

 already been observed by Swammerdam and Lyonet, and 

 even by Malpighi ; but the valvular arrangements and the 

 lateral openings of its eight compartments, were first mi- 

 nutely examined by Straus. 



In the larva state, as in the simpler annelides, the 

 dorsal vessel has a more lengthened, narrow, thin, and 

 uniform appearance, than in insects which have arrived 

 at their chrysalis or at their imago state ; and we observe 

 this vessel to thicken its parietes, to shorten its extent, 

 and to perfect its internal valves, as the muscles of the 

 segments, during the metamorphosis, contract and imbri- 

 cate the consolidating integuments, and thus shorten the 

 whole trunk of the body. The eight chambers of the heart 

 appear, like the segments of the abdomen, to be inserted 

 into each other from behind, and the bilabiate valves, with 

 their free edges directed forwards, are formed by a reflection 

 inwards of the tough inner parietes of this vessel, and 

 as they are confined to the posterior or abdominal portion 

 of the heart or aortal trunk, there appears to be a pulsating 

 muscular sac for each segment. These cavities contract in 

 succession from behind forwards, and convey a thin, colour- 

 less serous fluid, abounding with large blood globules ; they 

 receive this blood posteriorly from the abdominal veins, and 

 each cavity (133. D. a. 5.) likewise receives two lateral cur- 

 rents poured into its posterior end from the cavity of the 



