24 ARKIV FÖR ZOOLOGI. BAND 8. NIO 9. 



and Eriocran ia (f ig. 38), which evidently push the food into the 

 pharynx each time the larvae close the mandibles; and 2) of 

 the hook-shaped bristles on the inner side of the maxillse of 

 Cemiostoma (fig.53) and Nepticula (fig. 556) and on palpiger and 

 labrnm of Tischeria (figs. 35 and 36). Especially in the latter 

 genus, palpiger and labrum form together a very remarkable 

 structure. A t the upper side of the palpiger there is an obli- 

 que ridge, at the median side of which 3 pairs of large hooks, 

 directed backwards, are inserted, the posterior one a iittle 

 in front of the labrum. On the lower side of the latter the 

 ridge is continued, and bears 3 pairs of similar hooks. In 

 this way a kind of funnel is formed in which the 6 pairs of 

 hooks only allow the morsels of food to pass in one direction, 

 i. e. into the pharynx. 



The common occurrence of the structures described above 

 amongst the mining larvse calls for an explanation, and I 

 venture to suggest the following. It is highly probable that 

 the free action of the mouth-parts is greatly inconvenienced, 

 if not prevented, in the mining larvse described above by the 

 epidermis of the leaf pressing closely against them, and that 

 the only movements possible are those of the mandibles and of 

 the entire head. If that be the case, it follows that it would 

 be difficult, or even impossible, for them to assure the safe 

 passage of the parenchyma detached by the mandibles into 

 the pharynx without the aid of the accessory structures de- 

 scribed above. 



3. The characteristic shape of the labrum of Ornix, Gra- 

 cilaria and, above all, of Lithocolletis makes it apparent that 

 they actually are used as saws. Many observers also record 

 how the mining larvse move the head from side to side when 

 feeding. 



This accounts for the shape of the edge and also for the 

 broad shape of the labrum; as it is obvious that, if the 

 edge is to be applied against the wall of the mine, it must 

 extend beyond the margin of the mandibles when closed, 

 which it also does. 



It is doubtful whether in Ornix and Gracilaria it can also 

 be used as a saw, especially in the former genus, in which it 

 is comparatively narrow, and in which the hypopharynx pro- 

 jects so considerably in front of it. 



