CIRCULATION OF THE BLOOD. 405 



ones are still contracted. Thence proceeds the apparent undulating 

 motion which is perceived in the heart through the integument of the 

 body. From the anterior free aperture of the aorta the blood is driven 

 by this motion into the lateral space of the body contiguous to the 

 aorta, and it thence passes into all the vacant spaces of this cavity into 

 the antennae, feet, and wings, and thence, being continually driven on, 

 it pursues its course at the sides of the body, until it has again reached 

 the ventral cavity, where it then becomes mixed with the fluid there 

 found, and which has been subsequently formed by the constant activity 

 of the intestine, and upon the next expansion of the individual cham- 

 bers it passes again upon its preceding course. 



239. 



The motion of the heart itself was observed by the earliest 

 anatomists. Malpighi even observed the contraction of the dorsal 

 vessel progressing from behind forwards, and Swammerdamm as well 

 as later anatomists have confirmed this observation. But as all con- 

 sidered the dorsal vessel as completely closed, it could lead to no insight 

 into the circulating system of insects, and all the observations upon the 

 manner of this motion of the dorsal vessel arrived at no important result. 

 Herold * alone, who made the dorsal vessel especially the object of his 

 investigations, recognised more distinctly its undulating motion. This 

 undulating motion may be readily understood from the recently 

 explained structure of the heart. Thus all the chambers do not simul- 

 taneously contract, but always one after the other, so that during the 

 contraction the posterior one drives its contents into the one before it, 

 and during its expansion again receives blood from the cavity of the 

 body. As this alternating contraction and expansion passes from one 

 chamber to the other, the motion of the entire heart, like the peristaltic 

 motion of the intestinal canal, appears to progress in an undulating 

 line, although the motion is not in the entire heart, but only in an 

 individual chamber ; but the motion of these chambers passes so quickly 

 from one to the other, that the first and the last frequently expand at 

 the same time, whilst those lying between still contract. With respect 

 to the number of the contractions and expansions, differences have been 

 observed in them, which partly, as in respiration, proceeded from the 

 temperature, and were partly dependent upon the stage of development. 



* Physiologische Untersuchungen iiber das RiickengcfiibZ der Insektcn. Mcii-b. 1823, 8vo. 



