92 Cincinnati Society of Natural History. 



the other two groups, with a break at the fourth stage like that which 

 occurs at the sixth stage in the other two groups. Then at the end of 

 the first stage the larva of L. robiniella, is .764 mm. long; at the end 

 of the second, 1.528 mm. ; at the third, 2.292 mm. But at the end of the 

 fourth stage, while the changes above indicated have taken place, the 

 larva is still of the same length that it was at the end of the third stage. 

 At the end of the fifth stage, however, it has again added the length of 

 the larva of the first stage (.764 mm.), and is now 3.056 mm. long; at 

 the end of the sixth, 3.82; at the end of the seventh, 4.58 mm. Thus 

 unlike the larvae of the other two groups this larva continues to grow 

 through its sixth and seventh stages, but does not grow in its fourth. 

 The fourth stage here is the representative of the sixth in the other 

 groups. I suggested, as to the greater development of the trophi and 

 feet of L. ornatella, as compared with the flat larvae, that this develop- 

 ment was probably connected with the habit of the species of cutting 

 its way out of its mine, and crawling awa}^ to pupate. But doubt is 

 thrown on this by the larvae of the cylindrical group, for their feet and 

 trophi appear in their last stage to be about as well developed as those 

 of L. ornatella, yet these larvae never leave their mines, but like the flat 

 larvae pupate in their mines, and seem to be unable to crawl when re- 

 moved from them. There appears to be no sufficient reason why these 

 organs are better developed in the cylindrical larvae than they are in 

 the flat group; but in both the cylindrical larvae, and in L. ornatella, 

 this development of the trophi and feet is accompanied by the change 

 in the form of the larva, and in the position of the head. The change 

 in the form of the trophi in the flat group is of the same character, but 

 not so great; nor is the change in the form of the larva, nor in the 

 position of the head so great. But I have not time to enter further 

 into these matters, and my chief object has been to show the ratios of 

 size and food of the several larval stages; the relation of the quantity 

 of food, to the increase of size in the several stages; and the relation 

 of both to the periodicity of ecdysis; and to illustrate the manner in 

 which the apparently sudden metamorphoses have been produced 

 gradually, by the rapid growth of some organs, and the arrested growth 

 or absorption of others. 



