6 ARKIV FÖR ZOOLOGI. BAND 8. N:0 9. 



genera and, as far as we know, this phenomenon is always 

 combined with the presence of two well defined, and in some 

 respects entirely different, periods of the life of the larva. 



This difference consists in the two methods employed by 

 the larva? when feeding and making their mines. 



One method, the most specialized one, is to cut a thin 

 horizontal seetion in the parenchyma just below the upper 

 cuticle, or above the lower one; by this action the juice of 

 the celis, the walls of which are cut through, can be ab- 

 sorbed by the mouth parts of the larva and at the same 

 time, through the extension of the epidermis, the room 

 necessary for the larva is attained. 



This method is characterized by the larvse not feeding 

 on any solid food, but only on the sap of the leaf. 



The other method is to eat mouth-full after mouth-full 

 of the parenchyma, taking care not to vulnerate the epidermis, 

 and thus to excavate a mine. 



It is obvious that the latter method is the most primi- 

 tive, and does not require such a degree of modification of 

 the larvse as the former. 



And, as a matter of fact, in many genera employing the 

 latter method, and which we may call tissue-feeders, we 

 only notice comparatively small modifications in the mouth- 

 parts, changes in the form and size of the different organs, 

 and above all the presence of some accessorial structures. 



In the former larvse, which we may call sap-feeders, 

 on the other hand, some of the organs constituting the head 

 are either so strangely developed, or else reduced to such an 

 extent, that it is impossible, without comparative morpholo- 

 gical studies, to ascertain their homologies. 



The following investigation is recorded in such a way that 

 the different organs are treated separately throughout the 

 series of miners at my disposal. This is believed to render 

 it more easy to follow the gradual modifications of the organs, 

 but has the drawback that it is more difficult then to 

 comprehend the entire organisation of the mouth-parts of 

 each form. This will, however, in this paper, only occasionally 

 be entered into as it would for that purpose be necessary to 

 extend the investigations to a more minute study of the 

 anatomy and structure of the mines and the biology of the 

 miners than I have hitherto had an ojDportunity of doing. 



