3 
circulation of the blood in the class Vermes. 
of many of the blood vessels, and the course of the blood, 
but in some parts they are hid from our view, and are only to 
be detected by sudden coagulation of that fluid, which is 
effected by immersion in vinegar. I most readily confess, 
that had not Mr. Clift, the Conservator of the Museum 
of the Royal College of Surgeons in London, made sketches 
of the parts while in action, and given me his assistance, I 
probably should have failed in the investigation. The blood 
is brought from every part of the bgdy to a common trunk 
that supplies the organs of aeration, which are 26 in number, 
but does not all pass through them, a portion of unaerated 
blood going on towards the tail. 
The blood is propelled from the blood vessels of the organs 
of aeration with great force, these vessels performing the 
function of the ventricle of the heart in other animals ; it is 
carried to a large artery on the back in an aerated state, 
passes towards the head, from thence it is returned by a cor- 
responding vein on the belly, and before it arrives again at 
the organs of aeration, this vein receives supplies from two 
auricles furnished by the veins of the viscera; but there 
is no ventricle between the auricles and these organs. 
In the Lumbricus terrestris there is no heart, and the organs 
of aeration are not external, but consist of small lateral cells 
with an external opening, as in the leech, so that they can 
take no part in propelling the blood ; that office is entirely 
performed by the muscular power of the coats of the arte- 
ries. In this animal the circulation is very simple ; the artery 
upon the back, by its action, forces the blood up to the head, 
and it is returned by a corresponding vein upon the belly ; 
near the head there are five pair of lateral canals of commit- 
Bs 
