16 LICE AND THEIR MENACE TO MAN 



gut (Fig. 3, 5), which is a wide tube and corre- 

 sponds to the stomach of higher animals. It 

 has two capacious pockets (Fig. 3, 6) which lie 

 one on each side of the oesophagus and seem to 

 act as storage chambers for the blood, which can 

 be seen in them with the naked eye through the 

 body wall of the louse. The walls of the gut 

 contract and expand in waves, causing the con- 

 tents to flow backwards and forwards and to 

 keep circulating so that they are thoroughly 

 mixed with the digestive juices and come con- 

 tinually in contact with the wall, where the 

 nutriment is absorbed. These peristaltic move- 

 ments are a very noticeable feature in the louse, 

 in which insect the width of the gut in propor- 

 tion to its length is exceptional. Most insects 

 have the gut narrow and the necessary absorptive 

 surface is obtained by an increase in the length, 

 the gut being thrown into many coils like that 

 of a mammal. In such a gut the food passes 

 fairly continuously backwards, absorption pro- 

 ceeding as it moves. In the louse it moves to 

 and fro, and by this means the same effect is 

 obtained with the wide short gut. The fore-gut 

 narrows behind to form the hind-gut (Fig. 3, 11), 

 which runs forward again, forming an S-shaped 

 loop. Into this open the four long thin tubules, 

 the Malpighian tubes (Fig. 3, 10), which are 

 supposed to function as kidneys, to pass into 

 the gut waste products, which thus find their 

 way to the exterior. Farther back the hind-gut 



