FEEDING AND BREATHING 27 



and a study of the working of the parts of this region of the 

 food-canal shows clearly that the proventriculus acts as a 

 strainer ; it was long ago named the " honey-stopper '* by 

 the various writers on the anatomy of the hive-bee. Here 

 the organ is quadrate in cross-section, lined with four 

 prominent chitinous ridges which are separated by the 

 contraction of longitudinal muscles or approximated by 

 the contraction of circularly arranged fibres. This quadrate 

 " stomach-mouth " can be seen to close and open rhythmic- 

 ally when the digestive tube is slit up in a freshly killed bee. 

 Pollen-grains are thus allowed to pass on into the stomach, 

 the chitinous lining of the proventriculus bearing hair-Uke, 

 backwardly directed outgrowths which prevent the return 

 of solid particles into the crop. The liquid nectar or honey 

 can, however, be forced in either direction, as the need for 

 digestion, absorption, or storage may require. 



While in the crop, the food is mixed with saliva or 

 spittle, secreted by the insect's salivary glands (Fig. 10, sg)y 

 which lie on either side of the gullet and open by special 

 tubes or ducts into the median tube which enters the mouth 

 between the tongue and the labium. It is noteworthy that 

 the salivary ducts, being outgrowths of the fore- gut, have a 

 chitinous lining which is often spirally thickened as in an air 

 tube. The cells of the glands contain large bent elongated 

 bodies, the secretory capsules, which may be nuclear in 

 their nature. The saliva is an alkaline fluid containing a 

 diastatic ferment which acts on carbohydrate food materials. 

 A reservoir for storing saliva between feeding-times is 

 usually associated with these glands, which are very much 

 larger in plant-eaters than in insects of prey. In bees they 

 are remarkably numerous and complex, and their secretion 

 is partly effective in transforming the nectar sucked from 

 blossoms into honey, the cane sugar (sucrose) of the former 

 being ** inverted " to levulose and glucose. But this action 

 is mainly due to ferments or enzymes (sucrase) present in 

 the gastric juice, which, formed in the middle gut or 

 stomach, is passed forward into the crop. The nectar 

 sucked by bees from flowers is stored in the crop, which is 



