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 tw^o extremes in size, together "with 

 a caterpillar of medium size, "were photographed. The 

 smallest caterpillar as here sho"wn has not molted. The 

 medium caterpillar has molted t-wice. The largest has 

 molted four times and is approaching the fifth molt. 



