Practical Course. : 83 
Examine the appendages which surround the mouth 7 si¢u with a lens, 
so as to see how they lie with regard to each other. Then pull them out 
carefully one by one with forceps, beginning from behind, and notice 
that they consist of the following :— 
(1) A jointed bilobed flap (labium), with a three-jointed appendage 
(palp) attached to each side of it. 
(2) A pair of broad bilobed appendages (mazxillz), each with a five- 
jointed appendage (palp) attached to its side. 
(3) A pair of hard-toothed jaws (mandibles.) 
(4) A movable flap (labrum), which closes the mouth in front. 
(5) A fleshy tongue (lingua) which is an out-growth of the front 
portion of the digestive tract. 
Examine the spiracles, or openings of the breathing organs, on either 
side of the body. There are two large ones on each side between the 
bases of the legs, which the students may be able to make out with the 
help of a lens, if the specimen is fresh, There are also eight pairs of 
stigmata situated on the sides of the abdomen between the margins of 
the plates; these are more difficult to make out. 
Carefully cut off the wings close to the base, and notice the dark 
longitudinal streak which extends up the centre of the back of the thorax 
and abdomen. The streak indicates the position of the dorsal vessel, or 
heart, which lies immediately underneath the armour plates. 
Now pin the specimen, ventral surface downwards, to the weighted 
bark, inserting the pins into the bases of the legs, so as not to interfere 
with the dissection of the body. Immerse in water deep enough just to 
cover the specimen. Dissect off the whole of the dorsal plates, taking 
great care not to cut into the organs lying below. 
On cutting off the plates a layer of whitish fat will be exposed, with 
a, dark longitudinal space running up the middle line. The dark longi- 
tudinal space contains the dorsal vessel, but as the walls of this organ 
are thin and transparent, and the blood is colourless, it is somewhat 
difficult to make it out. 
The dorsal vessel is a straight many-chambered tube which receives 
the blood from the cavity of the body through openings on either side, 
and by its rythmical contractions drives it forward towards the head. 
Now dissect off the fat carefully so as to expose the digestive tract, 
which should be uncciled and separated from the fat and net-work of 
tracheal tubes that surround it. Trace it up to the throat in front, 
taking care not to cut away the soft white salivary glands. Then clear 
it down to the posterior end of the abdomen. Notice that the digestive 
tract is a tube, extending from the mouth in front to the anus behind, 
and that it consists of the following parts: — 
(1) The mouth, into which the two pairs of diffuse white salivary 
glands pour their secretion. 
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