THE MARGUERITE FLY. 



41 



palisade parenchjnna, but they dip down now and then into the spongy 

 parenchyma, and, as it often happens, a large portion of a mine may be 

 wholly in the spongy parenchjTna immediately above the epidermis of 

 the lower surface. Often, when the food supply is limited, owing to the 

 size of the leaf, or when there are a number of larvae within one leaf, the 

 entire mesophyl or fleshy portion of the leaf is devoured. 



Length of Larval Life. 

 The length of the larval period, Uke that of the egg, varies with the tem- 

 perature to which it is subjected, and is in all probabiUtj' modified in 

 addition by the relative abundance of food. Of the number of larvae kept 

 under observation from the day of their hatching, 122 were successfully 

 followed to the day of their pupation, and are available. Sixty-one, or 

 one-half the total number, were mining in plants which were kept in the 

 insectary and were subjected to a temperature similar to that to which the 

 eggs were subjected. The remaining 61 were subjected to a temperature 

 which was, on the whole, much higher (unfortunately the exact temper- 

 ature is not available) than that to which the first lot was subjected, the 

 plants which they were infesting being kept in a room adjoining the 

 insectary. Again, those in the insectary were followed during November, 

 and the plants in which they were feeding were inclosed within cheesecloth 

 bags to avoid further infestation. The second lot, on the other hand, 

 were followed during February; and as the plants in which they were 

 feeding were kept- in a room which was free of adult fhes. they were not 

 covered. In both series the killing of larvae other than those which were 

 being followed had to be resorted to from time to time in order not to lose 

 track of the others. 



Table I. — Length of Larval Life of 61 Larvae in the Insectary during 

 November, at a Temperature of about 55° at Night and of about 6')° 

 to 70° during the Day. (See Temperature in Connection with Length 

 of Egg Stage.) 



Number of Larv^. 



Length 

 of Life 

 (Days). 



11 



nii 



12 



12H 

 13 



mi 



14 



Number of Larv.*:. 



5, 



4 



1 



3 



2 . 



1, 



1 



Length 

 of Life 



(Days). 



143^ 

 15 



15J2 



16 



mi 



17 

 IS 



