SECT, ix EXCRETORY AND OTHER GLANDS 131 



inclined to consider them as occasional abnormal 

 returns to the Annelidan method of developing the 

 setae (see pp. 87, 88). When such an abnormal 

 setiparous sac does occur, it would in all probability 

 be utilised for excretory purposes. Chitin itself is 

 probably an excretory product, utilised for protective 

 purposes. 



FIG. 31. Part of a section through the gnathobase of Apus mentioned in the text 

 (p. 130), showing an abnormal reappearance of a setiparous gland containing 

 a brown secretion. , the nerves to the hairs ; those to the feathered hairs send 

 a fibre into each barb and possess small groups of ganglion cells. 



This irregular appearance in Apus of glands so 

 obviously homologous with the setiparous glands of 

 the Annelida, as an occasional abnormal return to a 

 former method of developing setae, establishes beyond 

 all contradiction the usual homology of the leg or 

 coxal glands of the Crustacea with the setiparous 

 glands of the Annelida. 



K 2 



