Manchester Memoirs, Vol. xlvii. (1903), No. 4. 5 



Fig. 3. — Complicated fortress with II exits. 

 a. — Apex of the tunnels. 



N.— Nest. 



Fig. 4.— Complicated fortress with several blind terminals. 

 a. — Apex of tunnels. 



N.— Nest. 



These plans show that sometimes the fortresses are ex- 

 tremely complicated, and sometimes very simple, but in no 

 case have I found one to tally exactly with the time- 



