FORM, GROWTH, AND CHANGE 59 



abdominal segments there is a pair of laterally-situated spiracles 

 so that including the prothoracic spiracles already mentioned 

 the caterpillar has nine of these air-openings along either 

 side of its body (Fig. 29 d.) 



Turning now to the internal organs of the caterpillar, some 

 remarkable and suggestive contrasts to the corresponding 

 structures in the butterfly may be noticed (Fig. 30 A). The 



^)- -T 



FIG. 32. 



A, Diagram of a Caterpillar's Silk-glands (gl) with their 

 reservoirs (r), ducts (d), and accessory glands (a, gl) ; pr, silk 

 press ; l.m, its lateral muscles ; sp, spinneret. Magnified. 



B, Silk-gland in cross-section ; ep, epithelium ; i, tunic ; int. 

 chitinous lining. C, A cell of the glandular epithelium in surface 

 view with its branched nucleus (n). Highly magnified. In 

 part after Helm, Zeitsch. f. Wiss., Zool. XXVI. 



food-canal runs straight through the body from mouth to anus, 

 and while the fore-gut (gullet and crop] and the hind-gut 

 (intestine and rectum) are relatively small, the mid-gut (stomach, 



