42 



MASS. EXPERIMENT STATION BULLETIN 157. 



It is thus seen that there is quite a variation in the period of growth or 

 development of the larvse, independently of temperature. Food supplj' 

 probablj' accounts for some of this variation. 



Table II. — Length of Life of 61 Larvcv in the Room, adjoining the Insectary 

 during February, at a Temperature, on the Whole, much Higher than 

 that during November. 



Number of Larv^. 



11, 



23, 

 4, 

 8, 

 15, 



Length 

 of Life 



(Days). 



6 



7 

 7.4 



Number of Larv.e. 



4, 

 1, 

 2, 



2, 



Length 

 of Life 

 (Days). 



9 

 10 



11 



A comparison of the two tables will show at once the difference in the 

 lengths of the larval periods of the larvae of the two lots, due to difference 

 in temperature. It should be noted also that there was almost as great 

 a range of variation in the development of the individuals of this lot as in 

 that of the first. 



PUPARIUM AND PuPA. (PlATES II. AND III.. FiGS. 7, 8, IL) 



Pupation takes place witliin the larval mine and inside the last larval 

 sldn, the latter thus becoming a puparium. The larva when full grown 

 merely shortens up and becomes inactive. Before becoming inactive, 

 however, it deepens slightly that portion of the mine in which it is to 

 come to rest, forming a more comfortable bed or resting place for itself, 

 as one might say. Having done this, it turns upon its dorsal surface and 

 gradually assumes a state of inactivity, becoming yellowish-white opaque 

 at the same time. 



The puparium, at first of the color of the contracting maggot or larva, 

 — pale j'ellow, • — becomes in time dull pale yellow or straw color, or it 

 turns to reddish brown, brown and dark brown, darkening with age. It 

 is easily perceived by the unaided eye tlirough the pale, semitransparent 

 epidermis on either surface of the leaf (Fig. 11). Normally it is completely 

 covered bj' the epidermis, only the minute cephalic spiracles at the exti-eme 

 anterior end projecting. The caudal or anal spiracles are completely 

 covered, and are not visible on the surface. Dr. Lintner must have mis- 

 taken the cephahc spiracles for the anal, in stating that the latter are 

 "thrust outward" through the epidermis. (Fourth Report on the In- 

 jurious and Other Insects of the State of New York, 1888, pp. 74, 75.) 



The apparent displacement of the cephalic spiracles (see larva) is brought 



