Annual Address of V. T. Chambers, Esq. 83 



Clem., as our example: ifin the latter part of June,, or in July or August, 

 we examine the leaves of the poison oak {Rhustoxico dendron) we shall 

 find the upper surface of many of them marked with solid whitish 

 blotches, of various sizes, the largest as much as an inch long, by ^ of 

 an inch wide, and perhaps with two or three branches; the smallest 

 barely perceptible specs. These are the mines of L. guttijinitella, and 

 the largest may contain half a dozen larvte, whilst the smallest have 

 only one, the large mines having become confluent with others. Look- 

 ing closely, or with a lens, we ma}- detect a minute glistening paint on 

 the leaf at the beginning of each mine; this is the egg shell. It is a 

 structureless membrane, containing a few minute pellets of "frass" or ex- 

 crementitious matter. The agg unhatched has never been seen on a leaf, 

 but I have dissected it out of the moth. It is oval, flat, with yellowish 

 contents, and is .304'2 millimeters long, and as the larva, like other larvne, 

 lies no doubt in a curved position in the Qgg^ it is a little longer than 

 the latter, probably about .3744: mm. long, which we shall presently see 

 is just what its length ought to be if the same ratio of growth prevails 

 in the first as in the succeeding four stages of its life; the youno-est 

 larva that I have measured, however, was already several hours old, 

 and measured nearly .4 mm. At this period of its life the mine is a 

 small, whitish speck. Holding the leaf up in the light we see that the 

 frass, as the excrement is technicall}^ termed, is deposited in the form of 

 the letter Y, and the larva lies in the fork of the Y, curving its body 

 around and eating in ever}^ direction, so that when the larva has attained 

 its full size at the end of its first stage of growth, the mine is usually 

 exactly circular. Tlien at this stage (which xay observations lead me 

 to believe is sixt}' hours after the time the larva left the ^gg) it ceases 

 to feed, and retiring to the center of the mine lies quietl}' across the 

 forks of the Y to undergo its change into the next larval stage. The mine 

 now is circular, with a diameter of 1.19 millimeter, with therefore an area 

 of 1.112 mm., which, since the larva only eats the superficial layers of 

 the parenchyma, in all of its stages as before said, represents actually 

 the size of the pile of food consumed in its first stage. The length of 

 the larva is now .8128 mm., or, .19 mm. less than fds the diameter of 

 the mine, but it is difficult to give the diameter of the mine accurately to 

 minute fractions of a mm., and the larva looks to &e just fds the diame- 

 ter of the mine in length. These are not fancies, nor the result of ac- 

 cidental coincidences in a few cases; thej^ are accurate measurements 

 of numerous larvse and their mines. It will be found that the length 

 of the larva always bears the same definite ratio to the diameter of the 

 mine: that the size of the mine bears always the same definite ratio to 



