The Age and Growth of some Eels from a Worcestershire Pond. 17 
One controls the operation by replacing in creosote, repeating 
this till all the zones are clearly visible. It is best to grind down 
only one otolith, keeping the other for control. 
The stone must be well rinsed after grinding each otolith, as 
fragments of linen adhere and cause the otoliths to break. The 
grinding down must be done very carefully, bearing in mind that 
one can grind away, but cannot replace. The first examination in 
creosote is a good guide as to the amount of grinding needed. 
Fig. 7. 
Fig. 8. 
It is only right to state that some otoliths give better prepara- 
tions than others and show the zones more clearly. Some are 
also thicker than others. In some one can count the zones without 
grinding down, or at most very slightly ; in others it is only after 
grinding down and examining in creosote several times that one 
can count them accurately. 
With otoliths of very large eels it is pretty well impossible .to 
count the zones exactly, as they are so close together. In some 
localities the otoliths appear to be more transparent than in others. 
An otolith examined with a low power in creosote, etc., shows- 
c 
