D-l 



•^^AiKUMii 



D-2 



D-3 



\liaj„ua^,..u^^ 



D-4 



D-5 



Figure 156. — Shell movements of type D are observed in the oysters poisoned by toxic substances or weakened by 

 adverse environment. D-5 shell movements of a dying oyster. Vertical ex'cursions of the writing pen are mag- 

 nified three times in all tracings. Uppermost level of the curves corresponds to closed shells. Time interval: 

 D-l, D-2, D-3, D-4, D-5, 1 hour each. 



E-l 



E-2 



Figure 157. — Shell movements of a spawning female. Note the frequencies of up and down movements, brevity of 

 the relaxation periods and slowing down at the middle of the downward strokes; this brief period coincides with 

 the penetration of eggs through the gills. Time interval: E-l and E-2, 1 minute each. 



THE ADDUCTOR MUSCLE 

 733-851 O— 64 12 



173 



