INSECTS 



from the two glands unite in a median thick-walled sac 

 known as the silk press (Pr), which opens to the exterior 

 through the spinneret. Two small accessory glands, which 

 look like bunches of grapes and which are sometimes 

 called the glands of Filippi (Fig. 155 A, B, C, GIF), open 

 into the silk ducts near their front ends. 



The relation of the silk ducts and the silk press to the 

 spinneret is seen in the side view of the terminal parts of 

 the labium and the left maxilla, given at B of Figure 155. 

 The silk press (Pr) is apparently an organ for regulating 

 the flow of the liquid silk material into the spinneret. It 



has been supposed, too, that it 

 gives form and thickness to the 

 thread, but the liquid material has 

 still to pass through the rigid tube 

 of the spinneret. 



The cut end of the press, given at 

 E of Figure 15 s, shows the crescent 

 form of the cavity (Lum) in cross- 

 section, and the thickening in its 

 roof (Rph), called the raphe. Mus- 

 cles (Mcls) inserted on the raphe 

 and on the sides of the press serve 

 to enlarge the cavity of the press 

 by lifting the infolded roof. The 

 four sets of these muscles in the 

 tent caterpillar are shown at C. 

 The dilation of the press sucks the 

 liquid silk into the cavity through 

 the ducts from the reservoirs, and 

 when the muscles relax, the elastic 

 roof springs back and exerts a 

 pressure on the silk material, which 

 forces the latter through the tube 

 tubules; oe, oesophagus; f tne spinneret. The continuous 



Reel, rectum; Vent, ventri- r 



cuius passageway from the ducts through 



[288] 



"M. 



Fig. 156. The alimentary 

 canal of the tent cater- 

 pillar 

 A, before feeding. B, after 

 feeding. Cr, crop; hit, in- 

 testine; Mai, Malpighian 



