14 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



stomach, or ventriculus (Vent), occupying half the length of the 

 body, and its walls are thrown into circular folds that evidently allow 

 of much expansion. The proctodaeum (Proc) is differentiated into a 

 short pyloric section (Py) into which open the Malpighian tubules 

 (Mai), a colon, or anterior intestine (AInt), and a large pear-shaped 

 rectal sac (Red). Clearly, the caterpillar did not inherit its alimentary 

 canal from its parents (cf. fig. 4). It has been provided with a 

 digestive system adequate to handle all the food it can eat, and there 

 is no limit to its appetite. In a tent caterpillar with a full stomach 



Mai 



Rect 



An 



Phy 



Mtli7 fcr 

 SceGng 



Fig. 7. — Internal organs of a caterpillar, except the fat tissue, exposed from 



the left side. 



alnt, anterior intestine; An, anus; Br, brain; Cr, crop; DV, dorsal blood 

 vessel ; Mai, Malpighian tubules ; Mth, mouth ; Oe, oesophagus ; Phy, pharynx ; 

 Proc, proctodaeum; Py, pylorus; Rect, rectum; skGld, silk gland; SoeGng, 

 suboesophageal ganglion; Stom, stomodaeum; Vent, ventriculus (stomach); 

 VNC, ventral nerve cord. 



(fig. 8 A) the latter (Vent) may extend from the thorax into the 

 seventh segment of the abdomen. In an individual just after a meal 

 (B) the crop (Cr) is expanded to a long sac more than twice its 

 length before eating, and the stomach is correspondingly shortened. 

 Crowell (1943) found that a measured amount of food goes through 

 the alimentary canal of the fifth or sixth instar of the southern army- 

 worm in about 3^ hours. During resting periods the fore gut is cleared 

 of solid food. 



Experimental studies on the feeding reactions of caterpillars and 

 their senses of smell and taste have been described by Dethier in a 

 series of papers (1937, 1939, 1941a, 1941b). Odor is shown to be 

 the principal factor by which a phytophagous caterpillar recognizes its 

 food plant. The olfactory sense organs are on the terminal segments 

 of the antennae and maxillae. The caterpillar's perception of odor is 

 of very short range, but its head is always close to the feeding surface. 

 In a study of Papilio larvae, which feed almost exclusively on umbel- 

 liferous plants, Dethier shows that the attractive odor is that of the 



