138 



entirely so. Starting from a common point, or nearly so, they 

 diverge from each other to converge and meet again in the lat- 

 ter part of the last larval stage. (In illustration of these life- 

 histories it will be necessary to refer again to the figures on 

 page 83. In fig. 2 I have not made the dentation of the man- 

 dibles distinct enough.) 



Concealed as these larvse all are within their mines, inside of 

 leaves, and dying as they inevitably do when removed from the 

 mines, it is somewhat difficult to trace accurately all the larval 

 changes ; but by watching them closely, by collecting large 

 numbers of larva? in all stages of growth, and comparing them, 

 and by pursuing the same process with the cast skins in the 

 mines, and counting them, I believe that I have succeeded in 

 tracing the larval histories of many species ; and while the lar- 

 val history of each group is materially different from that of the 

 others, that of the species of either group does not differ in any 

 important respect from that of others of the same group. 

 There are, however, many points common to all the groups, 

 and I give these first, accompanied by some general remarks 

 upon their characters and affinities, and followed by a statement 

 of the points peculiar to each group ; giving thus a brief life- 

 history of the genus, and of each of the three groups, rather 

 than life-histories of separate species ; together with notices of 

 such relations of the genus to others as seem to be indicated by 

 the larval characters. 



I have never seen the unhatched ego- of Lithocolletis ; but 

 upon the spot at which the mine begins, and while the mine is 

 yet scarcely visible to the unaided eye, may be seen, under 

 the lens, a glittering point. This is the shell, or rather cho- 

 rion. It is perfectly flat, and one might almost say that it 

 is imbedded in the substance of the leaf; its outline is oval, 

 and it does not vary much in size in the different species, being 

 usually about 0.34 mm. long and half as wide. The mine begins 

 under the egg, the larva passing obliquely into the leaf because 

 the structure of the head and troplii is such that it cannot enter 

 the leaf vertically, as do the larvge of some other genera. As 

 shown in figs. 1 and 2, the head of the larv£e of the flat group 

 projects straight forward and can neither be elevated nor de- 



