58 
BLOOD CIRCULATION. 
which surround it and join the dermal skeleton. 
Beneath are situated the complicated muscular plates, 
which are designated by Lyonnet as wings, not con- 
nected with the dorsal vessel, but which form a 
diaphragm, separating the body of the bee into two 
very unequal divisions, the smaller, or dorsal, above, 
and the larger, or visceral, below. The muscles of 
this diaphragm are very complicated, for besides the 
intercrossing of the muscular fibres on each side, 
under the dorsal vessel, there are even on the same 
side complex inosculations^ among themselves. 
This pericardial diaphragm., as Graber (52) calls 
it, in contracting drives back the viscera, and in con- 
secjuence of the enlargement of the upper or peri- 
cardial cavity resulting from it, the blood is forced 
through the opening into the dorsal vessel. This rests 
on the yellow pericardial nucleated cells, 0*035 mm. 
in diameter, forming a cushion. Sometimes these 
extend filaments to the outer layer of the heart, or the 
diaphragm. There are also fatty bodies {Fettkorper , 
Graber, or corps graisseux, Girard), containing here 
and there what Graber calls ‘ eingesprengte zelle7i ’ 
{cellides enclavees, Girard), or enclosed cells, of yellow 
colour, always with a single nucleus, resisting the 
action of acid and alkaline solutions. Amongst these 
there are nerve filaments and numerous tracheal 
ramifications, covering the dorsal vessel, and inter- 
calating themselves between the pericardial cells. 
* Union of two vessels of an animal body at their extremities, 
or by contact and perforation of their sides, by which means a 
communication is maintained. 
