254 ELEMENTARY BIOLOGY. [CHAP. 



bone is the best for seeing the essential struc- 

 ture. 



a. The Haversian canals : round or oval spaces, 

 usually rilled with dirt in grinding down the 

 bone, and therefore black and opaque, but 

 sometimes clear and empty. 



ft. The lamella: a series of concentric layers 

 round each Haversian canal. 



y. The lacuna: oval black spots between the 

 lamellae. 



3. The canaliculi : minute black lines seen radi- 

 ating from the lacunae. 



e. Besides the lamellae above mentioned others 

 will be seen which belong to no Haversian 

 system, but either fit in the angles between 

 the systems, or run around the outer surface 

 of the bone. 



b. Examine with -J obj. Observe the lacunae and 

 canaliculi more accurately. 



c. Examine in water or glycerine a thin transverse 

 section of a long bone which has been softened 

 by dilute acid. 



a. The Haversian canals empty or containing a 

 granular mass. 



/?. The lamella: very indistinct. 



y. The lacuna seen as transparent oval spaces. 



8. The canaliculi transparent and almost invisible. 



d. Examine sections of softened bone which have 

 been stained with carmine : in each lacuna will 

 be found a stained mass of protoplasm. 



