SECTION IX 

 Excretory and Other Glands 



The Shell gland. — The most conspicuous glands 

 of the Apodidse, the long coils of which are seen in 

 the shield, one on each side of the middle line, are 

 known as the shell glands. These are generally 

 homologised with the Annelidan nephridia. 



From Figs, i and 2 it will be seen that we have 

 assumed that the acicular gland of the dorsal para- 

 podium of the fifth segment became excretory, and 

 grew into the growing shell fold, thus forming the 

 shell gland. The position of its external opening, at 

 the tip of the dorsal branch of the second maxilla, 

 agrees exactly with this supposition. The distal end 

 of it is a chitin-lined sac running through the shaft 

 of this limb.^ The proximal end of the gland has 

 grown into the shield, and is of great length, being- 

 folded six times upon itself That the inner part of 

 the gland has grown upwards, and the limb bent 

 downwards, can be seen by the course of the duct of 

 1 See Appendix IV. for the finer structure of the gland. 



