M-2 



MEROMIXIS 



A condition of permanent stratification of 

 water masses in lakes. 



MESOLIMNION 



(Thermocline) 



METABOLISM 



The sum of all chemical processes occurring 

 within an organism; includes both synthesis 

 (anabolism) and breakdown ( catabolism ) of 

 organic compounds. 



METALIMNION 



(Thermocline) 



METAMORPHOSIS 



Abrupt transformation of an animal from one 

 distinctive life history stage to another 

 in its postembryonic development; e.g., 

 larva of an insect to a pupa . (See Life Cycle ) 



MICROORGANISMS Those minute organisms invisible or only barely 



(Microinvertebrates) . .., , ,, . 



visible to the unaided eye. Microorganisms 



pass through a U. S. standard series no. 30 



sieve but are retained on a no. 100 sieve 



(openings of 0.149 mm). (See Macroorganisms) 



MOLT 



To cast or shed periodically the outer body 

 covering which permits an increase in size. 

 This is especially characteristic of inverte- 

 brates. (See Ins tar) 



MOTILE 



( Free-Swimming ) 



