Practical Course, 85 
from Lower Bengal, where only smaller varieties are obtainable. The 
largest available full-grown specimens should be procured. They can 
be killed by dropping them in spirit, where they can be preserved until 
required for dissection, but the fresher they are the better. If it is neces- 
sary to preserve them for any length of time in alcohol before dissections 
each specimen should be pricked in several places with a needle to help 
the spirit to make its way into the tissues. ; 
Examine a specimen carefully with a lens and notice that it consists 
of the following parts :— 
(1) A round head, which bears the minute antennwy, eyes and 
mouth parts. 
(2) A thorax, consisting of three segments (prothorax, mesothorax, 
and metathorax), each of which bears a pair of jointed 
legs. These are the true legs, corresponding to the legs 
of the cockroach. 
(3) An abdomen, in which the students will be able to make out 
about nine segments. The two anterior segments are 
without limbs. The four following segments (Nos. 3 to 
6 inclusive, counting from before backwards) each have a 
pair of fleshy prolegs attached to them. Behind these are 
two segments: (Nos. 7 and 8) without limbs. No. 8 has 
a small mid-dorsal spine. Last of all is a collection of 
somewhat indistinct segments bearing the last pair of 
fleshy prolegs. 
Notice the nine pairs of button-like openings (spiracles) which are 
connected with the breathing tubes (trachew) that ramify through the 
body. They are situated on each side of the body, The anterior pair 
lies on the prothorax, while each of the anterior eight segments of the 
abdomen bears one pair. 
Notice a faint longitudinal streak along the middle of the back. 
This is due to the dorsal vessel (heart), which lies immediately below the 
integument. It is liable to be missed in rough dissection, In a living 
specimen its rythmical pulsation can easily be seen through the interven- 
ing tissues. Its function is to pump the blood towards the head. 
Now make a sketch in a note-book indicating what has been seey 
and marking each part with its name. 
Pin the caterpillar, ventral surface downwards, on to the weighted 
bark, inserting the pins into the anal prolegs and the sides of the thorax, 
so as not to interfere with the internal organs. Immerse tke bark in 
water deep enough just to cover the specimen. Carefully open up the 
body cavity by cutting down the mid-dorsal line with a pair of pointed 
scissors, Dissect back the flap on either side, taking great care not to 
injure the organs which lie below. Pin back the flaps, dissect off the 
