60 



blood space. Wi\y tlie difference, I do not know. 



The development of the gland of the adult, so far as 

 I cin detormine, is as follows:- Yrtien the snail Teredo 

 have been in the wood for a day or so, the gland of the 

 larva sends out processes which invade the surroiinding ec- 

 todermal tissues (the mantle, sides of the body). As the 

 side of the body becomes enlarged, it fuses with the dor- 

 sal sides of the gill filaments (fig. 27). From the first 

 there is close association between the gland and the gill. 

 As the latter grows, the filaments become invaded by the 

 gland; and as the anterior ten filaments become separated 

 from the rest of the gill, the two parts of the gland re- 

 main connected together by a long, narrow duct which ac- 

 companies the epibranchial canal and lies in the afferent 

 branchial vein (figs. 28-32). With the separation of the 

 tyro parts of the gill, the intervening part of the gland 

 disappears in X. fimbriata and T. navalis, but persists 

 in T. norvegica. As the gland enters the gill lamina, it 

 remains connected by a small duct with the main duct, and 

 sends the granular cells into tb.e latter. The main duct 

 may become gorged with granular cells (fig. 47). However, 

 in most cases there are few cells in it, and I am inclined 



