EXCRETION BY THE KIDNEY. 421 
taceans as the crayfish the green gland is supposed to repre- 
sent a kidney. It does not open into the body cavity like the 
preceding and the following form of the organ. It is well sup- 
plied with capillaries. The organ of Bojanus (Fig. 306) is the 
Fia. 326.—Blood-vessels of Malpighian bodies and convoluted tubes of kidney (after Sappey>. 
1, 1, Malpighian bodies surrounded by capsules ; 2, 2, 2, convoluted tubes connected with 
Malpighian bodies ; 3, artery branching to go to Malpighian bodies ; 4, 4, 4, branches of 
artery ; 6, 6, Malpighian bodies from which a portion of capsules has been removed ; 
7. 7,7, vessels passing out of Malpighian bodies ; 8, vessel, branches of which (9) pass to 
capillary plexus (10). 
main excretory channel in many groups of mollusks. In in- 
sects the long, coiled Malpighian tubules, which open into the 
intestine, are believed to secrete both bile and uric acid. 
Among vertebrates, till the reptiles are reached, the kidney 
is a persistent Wolffian body, hence its more simple form. 
