2 Sir Everard Home’s account of the 
each of them, one of these is, the mode in which the blood is 
aerated. 
We are not in my opinion furnished with a sufficient stock 
of materials in comparative anatomy, to make out a correct 
arrangement of the whole system of nature, nor do I know 
the best plan upon which it can be made ; but, at present, I 
look upon the circulation of the blood, and the mode of 
aerating it, as one liable to the fewest objections. 
The brain and nerves, as they are the most essential organs 
in the animal oeconomy, appear to have a prior claim, but the 
difference of structure in those organs, and in the spinal mar- 
row, is too small to serve for this purpose. 
The heart and blood vessels are the parts next in import- 
ance, and necessarily vary more in their structure, so as rea- 
dily to give characters to a greater number of classes, which 
is a great advantage, I have made these remarks from a 
desire that the science to which I have devoted much of my 
attention, should be pursued by those who engage in it, in the 
manner most likely to bring it to perfection, which is by sub- 
mitting to the drudgery of making out the structures of 
animals not yet known, instead of grasping at the whole 
system, so many parts of which we are unacquainted with. 
This attempt resembles that of the giants of old, in the alle- 
gory, who foolishly believed, when they got hold of the lower 
links of the golden chain which hung down from heaven, that 
they had acquired the means of getting possession of the 
power by which it was suspended. 
The circulation of the blood in the Lumbricus marinus, is 
probably the same as in all the vermes with external organs 
of aeration. The transparency of the animal shows the action 
