PHYSIOLOGY OF THE DORSAL VESSEL. 651 
and second chamber. But besides the blood which enters 
the second chamber in this way, the latter has received 
blood, during its diastole, through its auriculo-ventricular 
openings. The second chamber then contracts, and the blood 
is prevented from passing backward by the inter-ventricular 
valves between it and the posterior chamber; it therefore 
enters the third chamber, which dilates to receive it. The 
blood thus passes successively from chamber to chamber until 
it is poured out into the head, from which it returns to the 
abdomen.’ 
The above description of Straus Durckheim is not perhaps 
precisely accurate, but it appears to me by no means as absurd 
as Verloren pretends. 
Verloren has evidently entirely misunderstood the description 
given by the earlier writers, and although he has given a more 
detailed description, it differs from theirs rather in detail than in 
principle. He incorrectly represents the views of Straus Durck- 
heim, and attributes absurd statements to him which he after- 
wards shows are untenable. He admits that the dorsal 
vessel is constricted at intervals, but denies that the segments 
contract separately, and he describes the contraction as a 
wave which commences at the posterior extremity of the 
vessel and passes rapidly to its anterior extremity. The time 
occupied, according to Verloren, in the passage of the con- 
traction wave from the posterior to the anterior extremity 
is short as compared with the whole period of systole and 
diastole. So far, I think, Verloren is right, but the wave is 
certainly delayed at the junctions of the successive chambers, 
so that, although it travels forward rapidly, each chamber 
contracts in succession, and the more posterior chambers are 
fully contracted before those next in front commence contract- 
ing. Verioren figures the ostia and their valves and describes 
them with greater accuracy than Straus Durckheim, if Graber’s 
statements are correct, which is, I think, indisputable. 
Verloren also stated that the volume of blood in the dorsal 
vessel and its velocity increase as it moves forward, since each 
chamber receives a supply from the pericardium through its 
