142 



The period during which this formof trophi (fig. 2) lasts varies 

 in different genera and in different species of the same genus. 

 Thus, in Phyllocnistis, it lasts until the last larval stage, when 

 the form in fig. 4 is assumed, and the larva immediately spins 

 its cocoon. This is also the case in the flat and ornatella groups 

 of Lithocolletis ; but in the cylindrical group the change takes 

 place at the fifth stage, as it does also in Crraeilaria (^Parectopa) 

 robiniella Clem., and probably in other species of the Euspilap- 

 teryx o-roup of Gracilaria, while in such species as Gr. rhoisella 

 and G-. blandella, which I call true Gracilaria, it takes place at 

 the second stage. 



But while larvge having trophi as in fig. 2 must make linear 

 or flat mines, the converse does not hold good. Many larvae, 

 like those of Nepticula, Bedellia, Aspidisca and Antispila, make 

 linear mines, at least in their earliest stage, but the trophi of 

 these are of the ordinary type of lepidopterous larvte (fig. 4), 

 and the head is deflexed, the mouth not being fixed in the axis 

 of the body. But in such cases the mine is not a mere separa- 

 tion of the cuticle from the parenchyma ; the latter itself is eaten 

 out. Gracilaria robiniella and G. salicifoliella, after the moult 

 at which they assume the trophi as at fig. 4, also continue 

 making flat blotch mines, but the parenchyma is eaten out. In 

 these two species of Gracilaria and in others having similar 

 habits, the body never becomes cylindrical, but is always some- 

 what depressed, and the head is very flat and thin, even after 

 assuming the form of trophi, as in fig. 4. This form of trophi 

 is assumed sooner or later by all lepidopterous larvae ; in some, 

 as above shown, not until a late stage of larval life, in others 

 earlier. In the great majority of species it is assumed before 

 the larva leaves the egg ; if this is taken to indicate a high rank, 

 then Nepticula, instead of taking the lowest place among Tine- 

 ina, as in Ins. Brit., v. 3, should out-rank Lithocolletis and even 

 Gracilaria; andTischeria also would out-rank Gracilaria because 

 the larvae of Tischeria assume the form mven at fisi;. 4, either 

 before leaving the egg or at the first moult thereafter. 



In describing mines, they are frequently mentioned as being 

 either tentiform or flat. But from what is written above it will 

 be seen that this is not the true distinction. It is rather between 

 those in which the parenchyma is eaten out, and those in which 



