BRANCH ARTHROPODA ; CLASS INSECT A: THE INSECTS 169 



and in which the heart and tracheal " Vs " lie, and note 

 immediately underneath it the large coiled intestine with 

 a knot of greenish yellow threads in the centre. Carefully 

 uncoil and pin out the intestine, cutting away the tying 

 tracheae, but being careful not to cut other structures. 

 Work out the full length of the alimentary canal, noting 

 the oesophagus, the widened crop behind it, and the long 

 intestine. From the intestine arise several greenish 

 yellow threads, the Malpigliian tubules. These are the 

 excretory organs of the insect. What is the total length 

 of the alimentary canal ? 



The reproductive organs, consisting of a pair of glands 

 (egg-glands or sperm-glands) \vith a pair of tubes which 

 unite before reaching the body-wall and have a common 

 external opening, may now be seen. These should be 

 removed, thus exposing the ventral nerve-chain in the 

 abdomen. To expose the chain in the thorax it will be 

 necessary to pick away carefully the muscles. As in the 

 crayfish, the central nervous system in the beetle consists 

 of a ventral nerve-chain, a brain or supra-ccsopJiageal 

 ganglion and a pair of circum-acsophagcal commissures 

 connecting the brain and the foremost ganglion (infra- 

 ccsophageal) in the ventral chain. There are, in the 

 ventral chain, four ganglia in the thorax and four in the 

 abdomen. The large nerves running from the brain to 

 the compound eyes and to the antennae can be traced. 



Make a drawing showing the nervous system. 



Life-history and habits. The eggs, usually about 

 one hundred, are deposited in a silken sac or case which 

 is spun by the female, and either floats freely or is attached 

 to the under sides of the leaves of aquatic plants. This 

 egg-case is not wholly filled with eggs but has a consider- 

 able air-chamber in it, causing it to float. It is oval in 

 shape, and has a peculiar curved horn-like projection at 

 the upper end. In sixteen or eighteen days the young 



