20 



COMPARATIVE ANATOMY 



CHAP. 



Fig. 29.— Teredo Navalis in its boring, 

 ventral aspect (after Meyer and MolJius). 

 The centre is omitted, the calcareous tube 

 is for the most part uninjured. 



J- 



Pio. 30.— Shell of AsperglUirm (Ere- 

 chites) vaginlferum, dorsal view, a. An- 

 terior; p, posterior; d, right; s, left; 1, 

 siphonal aperture of the pseudoconch ; 2, 

 pseudoconch (calcareous tube) ; 3, true shell 

 embedded in the pseudoconch ; 4, anterior 

 aperture of the pseudoconch. 



