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PLATE 43. Variation in size of caterpillars of the same age- 

 Fifty caterpillars hatched from the same egg-cluster 

 were reared separately on lettuce leaves, all receiving 

 exactly the same treatment. When the caterpillars -were 

 five weeks old, the two extremes in size, together with 

 a caterpillar of medium size, were photographed. The 

 smallest caterpillar as here shown has not molted. The 

 medium caterpillar has molted twice. The largest has 

 molted four times and is approaching the fifth molt. 



