86 Elementary Manual of Zoology. 
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loose yellowish fat which is usually present in large quantities, and the 
following organs will be exposed :— 
(1) A thick straight digestive tract extending down the middle of 
the body, from the mouth in front to the anus, which lies 
in the last segment of the abdomen between the anal 
prolegs. 
(2) A delicate dorsal vessel or heart, which lies in the middle line 
above the digestive tract. This will very probably have 
been destroyed in opening up the cavity. 
(3) The silk glands, These are two long, firm, much convoluted 
organs which lie on either side of the digestive tract. 
They contain a fluid which hardens into silk when exposed 
to the air. 
(4) The numerous silvery trachea connected with the stigmata on 
either side of the body. 
Notice that the digestive tract is a tube opening at each end of the 
bedy, and that it consists of the following parts :— 
(1) The cavity of the mouth. 
{2) A narrow gullet. 
(8) A large dilated portion (stomach), which extends throughout 
the greater part of the body. 
(4) A narrow intestine into which open three pairs of slender 
thread-like excretory glands (malpighian tubes). 
(5) An expanded chamber (rectum) terminating in a posterior 
opening (anus), 
Dissect out the silk glands and trace the duct on either side which 
passes up into the mouth. 
Make a rough sketch in a note-book showing the organs exposed, cut 
off a small piece of one of the largest tracheal tubes that can be found and 
endeavour with a lens to make out the spiral filament by which it is kept 
in shape. 
Cut away the digestive tract at the gullet, pin it back out of the 
way. Pin the silk glands also out of the way on either side, and search 
for the chain of brilliantly white nerve ganglia which lie along the ven- 
tral surface of the body beneath the digestive tract. When this has 
been found, dissect away the tissues around it so as to expose it through- 
out its whole length, Notice the numerous nerves given off from each 
ganglion, and endeavour to make out the branches which pass round the 
gullet to connect the supraewesophageal ganglion, which lies in the head, 
with the sub-cesophageal ganglion, which lies below the gullet, and is the 
first of the ventral chain. 
