20 



COMPARATIVE ANATOMY 



CHAP. 



FIG. 29. Teredo Navalis in its boring, 

 ventral aspect (after Meyer and Motoius). 

 The centre is omitted, the calcareous tube 

 is for the most part uninjured. 



FIG. 30. Shell of Aspergillum (Bre- 

 chites) vaglniferum, 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. 



