7 
circulation of the blood in the class Vermes. 
of the organs of aeration, as of the heart itself, since the vessels 
that carry the blood to these organs are larger and weaker than 
those which return it to the heart, so that, instead of the blood 
being propelled into the organs of aeration by arteries, it is 
carried by veins, and propelled towards the heart by arteries. 
In proof of the correctness of my description of this kind of 
circulation, which I consider to be common to all that order, I 
have annexed two drawings of the heart of the sepia officina- 
lis ; they were made in the year 1787, by Mr. Bell, draughts- 
man to Mr. Hunter, and the preparations from which they 
were taken are preserved in the Museum, and it is with the 
permission of the Board of Curators that the present copies 
are laid before the Society. 
In the sepia, whose veins are of an enormous size, there is 
a bulb or swelling of the vein at the root of each of the organs 
of aeration, with a double valve to prevent regurgitation of 
the blood after it had once entered these organs ; to this is 
connected a spongy body, that does not appear to communi- 
cate with the bulb itself, the use of which I am unacquainted 
with. This peculiarity appears to be wanting in the teredines 
and other vermes, as not being required. 
The circulation of the blood in the lowest class of animals 
being the reverse in principle, to what it is in the higher 
classes, led me to consider, from what circumstances this 
change could be produced : and reflecting that the great 
difference, between animals of the higher classes and those of 
the vermes, is, that when the heart stops in the one, the ani- 
mal dies, but in the other, that this action can be restored, it 
led me to believe, that the peculiarities in their circulation pro- 
duce the means by which the action of the heart is renewed. 
Whether all the vermes upon any occasion go into a torpid 
