38 MASS. EXPERIMENT STATION BULLETIN 157. 



over the micropyle. It is somewhat variable in size: a number of meas- 

 urements taken showed a length of .25 to .33 miUimeter and a width of 

 .14 to .17 millimeter. Its length is, as a rule, slightly more than twice its 

 width. 



The segmented embryo is e^isily made out under Ihe compound micro- 

 scope in an egg somewhat advanced in its period of incubation. In a still 

 older egg the embryo is found to be already provided with its dark cliit- 

 inous rake or rasping organ, the dark color of which contrasts strongly with 

 the general paleness of the rest of the body. Another feature of such an 

 embryo is its restlessness. Shortly before hatching this restlessness or 

 activity is strongly marked. 



Length of Egg Stage. 

 The period of incubation is dependent upon the temperature at wliich 

 the eggs are incubated. To determine the length of this period eggs were 

 marked at the time of their deposition within leaves of plants in the in- 

 sectary, and these were then periodically examined for their batching. 

 In other instances, egg-laying females were confined within cheesecloth 

 bags for short periods, upon leaves on plants kept in the insectary, and 

 on others kept in the laboratory, and the eggs deposited in them were 

 then examined from time to time, as in the above cases, for their hatching. 

 The eggs incubated in the laboratory, where the temperature was higher, 

 hatched in from two and one-half to three days after they were deposited. 

 In the insectary, however, where the temperature approximated more or 

 less to that at which marguerites are kept, — about 55° at night and 

 about 65° to 70° during the day (it fell somewhat below and rose somewhat 

 above tliis both at night and during the day), — they hatched in from a 

 little over four and one-half to somewhat over five and one-half days. 

 The great majority, however, hatched in from nearly five to somewhat 

 over five and one-half days. The greater variation in the length of the 

 period in the insectary was probably due to the greater variation in the 

 temperature, — a condition which could not very well be avoided. There 

 is a record of a period of six and one-haK days in the case of two eggs. The 

 writer, however, cannot vouch for its correctness. The larva begins 

 feeding immediately after hatching. 



The Larva. (Plates I. and II., Figs. 4, 6.) 

 The larva or maggot mining within the leaves is colorless, the greenish- 

 yellow cast which marks the posterior half being imparted by the green 

 and black pellets of leaf tissue or food which in chain or strand like forma- 

 tions are visible through the body wall. In form it is subcyhndrical, 

 tapering anteriorly and posteriorly from the region of the fifth and sixth 

 segments, terminating subacutely anteriorly, and truncately posteriorly. 

 When fully developed it measures about 3.5 miUimeters in length and 

 .75 millimeter to slightly over in width across its stoutest portion. It is 

 composed of twelve segments. The first segment is very small and appears 



