LABRAL GLANDS OF SIMOCEPHALUS 223 



the food groove (PI. 10, fig. 13, and PI. 9 figs. 5 to 8). Each 

 seta is beset with a double row of hairs on its inner side. During 

 the movement of the maxillae the setae move backwards and 

 forwards and in their forward movement move inwards, so 

 that the hairs of the opposite setae meet in the food groove. 



At the hinder margins of the biting surfaces of the mandibles 

 there are blunt spines (Pis. 9 and 10, figs. 6 and 13), while the 

 anterior parts are scored with vertical serrated ridges. The two 

 mandibles, which are never symmetrically apposed to one 

 another, appear to work like two cog-wheels fitting into one 

 another and thus crush the food and at the same time force it 

 forwards into the beginning of the oesophagus, up which it 

 rapidly passes by peristalsis. 



The mechanism of the method of feeding is as follows : 

 food particles in the food-stream, drawn in by the action of 

 the united movements of the trunk-limbs, are diverted towards 

 the median groove along the side of the labrum, by the first 

 trunk-limbs. At the tip of the labrum they are caught by the 

 anterior setae of the gnathobases of the second trunk-limbs 

 and brushed dorsally into the food groove above the tip of the 

 labrum and between the maxillae. The brush-like setae of the 

 gnathobase are in all probability the main agents in bringing 

 this about. The more anteriorly-placed comb-like setae which 

 brush the side of the labrum also assist in collecting the food 

 on to the maxillae, but their chief function seems to be to brush 

 the secretion of the labral glands on to the food as it collects 

 between the maxillae. Hardy and MacDougall (8) state that 

 when the food is swallowed it consists of particles — ' which 

 are glued together by some sticky substance '. It is suggested 

 that this sticky substance is the secretion of the labral glands. 

 The food which collects as a bolus between the two maxillae 

 is now and again pushed forwards by the movements of the 

 appendages on to the mandibles. PI. 10, fig. 13, shows how the 

 hairs on the setae of the maxillae point forwards, and PI. 9, 

 figs. 6, 7, and 8, show how the hairs of the adjacent setae fit 

 together and so make an admirable broom for sweeping a bolus 

 forwards on to the mandibles. A movement of the maxillae 



