10 INTRODUCTION. 



markings on its wings ( Plate I, e, /,), deposits an egg- 

 on the under side of the celery leaf. This egg (a) is 

 a small, light yellow object, nearly spherical, though 

 slightly flattened where it is attached to the leaf. 

 A week or so after it has been laid there hatches 

 from it a small caterpillar or ' worm,' less than one- 

 tenth of an inch long, black, with two transverse 

 white bands — one across the middle of the body and 

 the other at the posterior extremity — and having 

 the back roughened with minute, black, projecting 

 points. This little caterpillar feeds upon the celery 

 leaf, and within a few days so increases in size that 

 it becomes necessary to shed its skin, or moult. For 

 this purpose the skin splits along the back and the 

 caterpillar walks out, clothed in a new skin that had 

 been formed beneath the old one. The color mark- 

 ings are somewhat different on this new covering. 

 The caterpillar continues feeding and growing for 

 several weeks, casting its skin at occasional intervals, 

 and changing considerably in color and markings. 

 When full grown it is of the form and size indicated 

 at b on the plate, the general color being pale green, 

 with a series of transverse bands of black and yellow 

 markings.. When irritated it thrusts out, from a slit 

 just back of the head, a pair of peculiar yellow Y- 

 shaped organs, that emit a disagreeable odor. These 

 organs are represented at b on the caterpillar, and at c 

 is shown a front view of the head, with them extend- 

 ed. They doubtless serve as a protection from vari- 

 ous enemies. 



