REPORT OP THE ENTOMOLOGIST. 227 



dark. Althoiigli active while in the mine, only the faintest rudiments 

 of legs are discernible. The mouth parts are very curiously modified. 

 Mandibles and maxillae are the only parts to be seen, and they appear 

 as figured at d. The mandibles seem admirably adapted for separating 

 the leaf layers. Though apparently both mandi])les are continuous, yet 

 in reality they are simply connected by a membrane which allows play, 

 and through an opening in which, on the ventral side, the food enters 

 the alimentary canal. Two pairs of rudimentary almost colorless eyes 

 can be seen under a moderate magnifying power, occupying the relative 

 position indicated in figure d. The hind pair usually consists of four, 

 five, or six large and apparently structureless cells, resembling fat cells. 

 Each one of the front pair consists of from two to four similar cells 

 though smaller. From the lateral edge of each segment projects a 

 rather long bristle, and just above the lateral edge there is a smaller 

 one. The last segment bears six such bristles. Between the lateral 

 edge of each segment and its dorsal plate are two short, stout tubercles 

 placed close together, and each surmounted by a short bristle.* The 

 spiracles are extremely minute, but with a high microscoiMc power 

 can be seen near the latero-anterior border of each of the abdominal 

 segments except the last, each with its minute tracheal branch running 

 to it. The meta and mesothoracic segments have none, but that on the 

 prothoracio is larger than any of tlic others and situated on the hind 

 border of the segment. 



When once removed from their mines these flat larvae have not the 

 power to re-enter the leaf and commence new mines. This is due in 

 great part to the peculiar structure of the mouth-parts, which are in no 

 way fitted for piercing a tough epidermis. Then, too, as Mr. Chambers 

 has suggested, the head projects straight forward and can be elevated 

 or depressed but very slightly, which also is the case with the modified 

 jaws. 



To one acquainted with the general features of the larvae of the dif- 

 ferent orders of insects, these flat larvae bear a much closer general re- 

 semblance to coleopterous larvae than to lepidopterous. The number ox 

 molts which they have undergone up to this time is difficult to ascer- 

 tain. Usually five cast-off skins can be readily found in a completed 

 mine, which;^ together with the skin which is cast within the cocoon (of 

 which we shall speak further on) and one or two small ones which have 

 become so decomposed and mixed with the excrement as to have be- 

 come indistinguishable, would indicate seven or eight molts. Mr. 

 Chambers's studies have led him to the conclusion that there are always 

 eight molts in LithocoUetis. He based this conclusion on the fact that 

 eight distinct sizes are discernible in the larvae of each species. He has 

 also noticed the following definite relation between successive mqlts: 

 "At each molt except the seventh, the length of the larva in its first 

 stage is added to that of the molting larva;" or, in other words, at 

 each molt the larva increases in length by just the length of the first 

 stage. I have been unable to verify this relation with the species under 

 consideration. 



When these flat larvae have attained full size they usually measure 

 ii'om four to five millimeters in length ; and their blotch mine covers a 

 space equal to from one-half to three-quarters of an inch square. At 

 its seventh molt, instead of coming out again a larger flat coleopter- 

 iform larva, its entire ai-i])earance cbnngesT It is longer than before, 

 and, instead of being flut, is cylindiical. Its mouth parts have assumed 

 amore^normal lepidopterous ibrm, and its eyes have become covered by 

 dark pigmentary layer. The regular fourteen feet in the normal posi- 



