\\ \l"\1\ \M) PHYSIOLOGY 





FIG. 165. Transverse section of the abdomen of a caterpillar, Pieris rapes, b, blood cor- 

 puscles; c, cuticula; d, dorsal vessel; /, fat-body; g, ganglion; h, hypodermis; /, leg;m, 

 muscle; mi, mid intestine, containing fragments of cabbage leaves; mt, Malpighian tube; s, 

 silk gland; sp, spiracle; tr, trachea. 



which the metamorphosis takes place; the amount of fat increases as 



the larva grows, and diminishes in the pupal stage, though some of it 



lasts over to furnish nourishment for the 



imago and its germ cells. The gradual 



accumulation of uric acid and urates in 



the fat-body indicates an excretory func- 



tion, particularly in Collembola, which 



have no Malpighian tubes. The intimate 



association between the ultimate tracheal 



branches and the fat-body has led some 



authorities to ascribe a respiratory func- 



tion to the latter. A close relation of some sort exists also be- 



tween the fat-system and the blood-system; fat-cells are found free 



in the blood, and the blood corpuscles originate in the thorax and 



B 



FIG. 166. Fat-cells of a cater- 



pillar, Pieris. A, ceils filled with 



