SECT, ix EXCRETORY AND OTHER GLANDS 



125 



the gland which, on leaving the shell fold, makes a 

 sudden sharp bend downwards. We thus consider 

 this shell gland as a striking link between our Annelid 

 and Apus. The mesoblastic origin of the urinary 

 canal may mean that this section of the gland is a 



FIG. 30. Diagram of the shell gland, h, the heart ; ac, the aorta cephalica. The 

 blood is distributed to the gland through^ a special vessel on each side, ts, 

 terminal saccule ; uc, urinary canal ; 6, chitin-lined bladder in the shaft of the 

 dorsal parapodium of the 2nd maxilla (///), homologous with the original 

 setiparous gland of the Annelid. 



new formation, the bladder alone representing the 

 acicular gland. 



This homology of the Crustacean shell gland with 

 the acicular gland of the fifth parapodium of the 

 Annelid, naturally leads us to ask whether the acicular 

 gland of any other of the head limbs has been pre- 



