No. 521] FACTS ABOUT THE « LOBSTER PEARL » 297 



minute vertical canals, which give passage to either 

 sense-organs (sensory setae, bristles or "hairs"), or to 

 glands (ducts of the tegumentary glands), and thus put 

 the soft and sensitive skin in direct relation to its outer 

 environment. The pores of the tegumental glands open 

 on crater-like elevations similar to those described 

 above, but lie far below the limits of visibility to the 

 naked eye. These glands themselves are usually not 

 over .15 millimeter in longest diameter, and while the 

 length of their ducts is not commonly more than .15 



mm., plus the thickness of the shell 

 diameter is only .DOS mm. The hair 

 hand, are sometimes visible, being .1 

 or larger, while many are much sm; 

 when the shell from the under side 

 seen from the inside, they are foun< 

 large blister like elevations (Fig. 4) 

 to show in the photograph. In oth< 

 shell from the upper side of the big 



t, their 

 e other 

 ameter 

 lis, and 



